diff --git a/src/locales/en.json b/src/locales/en.json
index 3c4d0fc..edf6e91 100644
--- a/src/locales/en.json
+++ b/src/locales/en.json
@@ -269,6 +269,8 @@
     "back": "Go Back",
     "loadMore": "Load more",
     "uploadFailed": "Image upload failed.",
+    "uploadErrorTitle": "Image Upload Error",
+    "uploadErrorConfirm": "OK",
     "uploading": "Uploading... (30 sec – 1 min)",
     "nextStep": "Next Step"
   },
diff --git a/src/locales/ko.json b/src/locales/ko.json
index 8afb089..16728d7 100644
--- a/src/locales/ko.json
+++ b/src/locales/ko.json
@@ -268,6 +268,8 @@
     "back": "뒤로가기",
     "loadMore": "더보기",
     "uploadFailed": "이미지 업로드에 실패했습니다.",
+    "uploadErrorTitle": "이미지 업로드 오류",
+    "uploadErrorConfirm": "확인",
     "uploading": "업로드 중 (30~60초 소요)",
     "nextStep": "다음 단계"
   },
diff --git a/src/pages/Dashboard/AssetManagementContent.tsx b/src/pages/Dashboard/AssetManagementContent.tsx
index 50e57a4..1c74671 100755
--- a/src/pages/Dashboard/AssetManagementContent.tsx
+++ b/src/pages/Dashboard/AssetManagementContent.tsx
@@ -3,6 +3,7 @@ import React, { useRef, useState, useEffect } from 'react';
 import { useTranslation } from 'react-i18next';
 import { ImageItem, ImageUrlItem } from '../../types/api';
 import { uploadImages } from '../../utils/api';
+import { isImageInputFile } from '../../utils/imageCompression.ts';
 
 interface AssetManagementContentProps {
   onNext: (imageTaskId: string) => void;
@@ -38,6 +39,20 @@ const AssetManagementContent: React.FC<AssetManagementContentProps> = ({
     }
   }, []);
 
+  useEffect(() => {
+    if (!uploadError) return;
+
+    const handleEscape = (event: KeyboardEvent) => {
+      if (event.key === 'Escape') {
+        event.preventDefault();
+        setUploadError(null);
+      }
+    };
+
+    window.addEventListener('keydown', handleEscape);
+    return () => window.removeEventListener('keydown', handleEscape);
+  }, [uploadError]);
+
   const handleVideoRatioChange = (ratio: VideoRatio) => {
     setVideoRatio(ratio);
     localStorage.setItem('castad_video_ratio', ratio);
@@ -100,9 +115,7 @@ const AssetManagementContent: React.FC<AssetManagementContentProps> = ({
   const handleDrop = (e: React.DragEvent) => {
     e.preventDefault();
     e.stopPropagation();
-    const files = Array.from(e.dataTransfer.files).filter((file: File) =>
-      file.type.startsWith('image/')
-    );
+    const files = Array.from(e.dataTransfer.files).filter(isImageInputFile);
     if (files.length > 0) onAddImages(files);
   };
 
@@ -146,6 +159,37 @@ const AssetManagementContent: React.FC<AssetManagementContentProps> = ({
         </div>
       )}
 
+      {uploadError && (
+        <div
+          className="asset-upload-error-overlay"
+          onClick={() => setUploadError(null)}
+        >
+          <div
+            className="asset-upload-error-dialog"
+            role="alertdialog"
+            aria-modal="true"
+            aria-labelledby="asset-upload-error-title"
+            aria-describedby="asset-upload-error-message"
+            onClick={(event) => event.stopPropagation()}
+          >
+            <h2 id="asset-upload-error-title" className="asset-upload-error-title">
+              {t('assetManagement.uploadErrorTitle')}
+            </h2>
+            <p id="asset-upload-error-message" className="asset-upload-error-message">
+              {uploadError}
+            </p>
+            <button
+              type="button"
+              className="asset-upload-error-confirm"
+              onClick={() => setUploadError(null)}
+              autoFocus
+            >
+              {t('assetManagement.uploadErrorConfirm')}
+            </button>
+          </div>
+        </div>
+      )}
+
       {/* Fixed Header - 뒤로가기 버튼 */}
       <div className="asset-sticky-header">
         {onBack && (
@@ -268,9 +312,6 @@ const AssetManagementContent: React.FC<AssetManagementContentProps> = ({
 
       {/* Fixed Footer - 다음 단계 버튼 */}
       <div className="asset-sticky-footer">
-        {uploadError && (
-          <p className="text-red-500 text-sm mb-2">{uploadError}</p>
-        )}
         <button
           onClick={handleNextWithUpload}
           disabled={imageList.length === 0 || isUploading}
@@ -283,7 +324,7 @@ const AssetManagementContent: React.FC<AssetManagementContentProps> = ({
       <input
         ref={fileInputRef}
         type="file"
-        accept="image/*"
+        accept="image/*,.heic,.heif"
         multiple
         onChange={handleFileChange}
         className="hidden"
diff --git a/src/styles/contents-social.css b/src/styles/contents-social.css
index 4fe937b..dad3794 100644
--- a/src/styles/contents-social.css
+++ b/src/styles/contents-social.css
@@ -689,10 +689,6 @@
   flex-direction: column;
 }
 
-.video-detail-header {
-  /* margin-bottom: 24px; */
-}
-
 .video-detail-back-btn {
   display: flex;
   align-items: center;
diff --git a/src/styles/studio-assets.css b/src/styles/studio-assets.css
index 47ea6f5..e3381e4 100644
--- a/src/styles/studio-assets.css
+++ b/src/styles/studio-assets.css
@@ -832,6 +832,72 @@
   gap: 0;
 }
 
+/* Upload Error Dialog */
+.asset-upload-error-overlay {
+  position: fixed;
+  inset: 0;
+  z-index: 1100;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  padding: 1rem;
+  background: rgba(0, 17, 18, 0.82);
+  backdrop-filter: blur(4px);
+}
+
+.asset-upload-error-dialog {
+  width: min(100%, 420px);
+  padding: 1.5rem;
+  background: #01393B;
+  border: 1px solid #379599;
+  border-radius: 20px;
+  box-shadow: 0 24px 64px rgba(0, 0, 0, 0.45);
+}
+
+.asset-upload-error-title {
+  margin: 0;
+  color: #94FBE0;
+  font-size: 1.25rem;
+  font-weight: 700;
+  line-height: 1.3;
+}
+
+.asset-upload-error-message {
+  margin: 0.75rem 0 1.5rem;
+  color: #E5F1F2;
+  font-size: 0.9375rem;
+  line-height: 1.6;
+  overflow-wrap: anywhere;
+  white-space: pre-wrap;
+}
+
+.asset-upload-error-confirm {
+  width: 100%;
+  min-height: 44px;
+  padding: 0.75rem 1rem;
+  color: #002224;
+  background: #94FBE0;
+  border: 0;
+  border-radius: 999px;
+  font-size: 0.9375rem;
+  font-weight: 700;
+  cursor: pointer;
+  transition: background-color 0.2s, transform 0.2s;
+}
+
+.asset-upload-error-confirm:hover {
+  background: #B8FFE9;
+}
+
+.asset-upload-error-confirm:active {
+  transform: translateY(1px);
+}
+
+.asset-upload-error-confirm:focus-visible {
+  outline: 3px solid #CFABFB;
+  outline-offset: 3px;
+}
+
 
 /* Fixed Header - 뒤로가기 */
 .asset-sticky-header {
diff --git a/src/utils/api.ts b/src/utils/api.ts
index 4caa1fd..80bdb3a 100644
--- a/src/utils/api.ts
+++ b/src/utils/api.ts
@@ -35,6 +35,7 @@ import {
   CommentItem,
   LikeToggleResponse,
 } from '../types/api';
+import { uploadImagesSequentially } from './imageUpload.ts';
 
 export const API_URL = import.meta.env.VITE_API_URL || 'http://40.82.133.44';
 console.log('[API] API_URL:', API_URL);
@@ -655,18 +656,10 @@ export async function uploadImages(
   imageUrls: ImageUrlItem[],
   files: File[]
 ): Promise<ImageUploadResponse> {
-  const formData = new FormData();
-
-  // URL 이미지들을 images_json으로 전달
-  if (imageUrls.length > 0) {
-    formData.append('images_json', JSON.stringify(imageUrls));
-  }
-
-  // 파일들을 files로 전달
-  files.forEach((file) => {
-    formData.append('files', file);
-  });
+  return uploadImagesSequentially(imageUrls, files, postImageUpload);
+}
 
+async function postImageUpload(formData: FormData): Promise<ImageUploadResponse> {
   const controller = new AbortController();
   const timeoutId = setTimeout(() => controller.abort(), IMAGE_UPLOAD_TIMEOUT);
 
@@ -677,19 +670,21 @@ export async function uploadImages(
       signal: controller.signal,
     });
 
-    clearTimeout(timeoutId);
-
     if (!response.ok) {
+      if (response.status === 413) {
+        throw new Error('이미지 파일이 너무 커서 업로드할 수 없습니다. 더 작은 이미지를 선택해주세요.');
+      }
       throw new Error(`HTTP error! status: ${response.status}`);
     }
 
     return response.json();
   } catch (error) {
-    clearTimeout(timeoutId);
     if (error instanceof Error && error.name === 'AbortError') {
       throw new Error('이미지 업로드 시간이 초과되었습니다. 다시 시도해주세요.');
     }
     throw error;
+  } finally {
+    clearTimeout(timeoutId);
   }
 }
 
diff --git a/src/utils/imageCompression.ts b/src/utils/imageCompression.ts
new file mode 100644
index 0000000..c031f43
--- /dev/null
+++ b/src/utils/imageCompression.ts
@@ -0,0 +1,249 @@
+export const MAX_UPLOAD_IMAGE_BYTES = 2 * 1024 * 1024;
+export const MAX_UPLOAD_IMAGE_DIMENSION = 2048;
+export const MAX_FALLBACK_UPLOAD_IMAGE_BYTES = 15 * 1024 * 1024;
+
+const OUTPUT_MIME_TYPE = 'image/jpeg';
+const OUTPUT_EXTENSION = 'jpg';
+const BACKEND_IMAGE_EXTENSIONS = new Set(['jpg', 'jpeg', 'png', 'webp', 'heic', 'heif']);
+const BACKEND_IMAGE_MIME_TYPES = new Set([
+  'image/jpeg',
+  'image/png',
+  'image/webp',
+  'image/heic',
+  'image/heif',
+  'image/heic-sequence',
+  'image/heif-sequence',
+]);
+
+interface ImageDimensions {
+  width: number;
+  height: number;
+}
+
+interface DecodedImage extends ImageDimensions {
+  source: CanvasImageSource;
+  dispose: () => void;
+}
+
+interface CompressionAttempt {
+  scale: number;
+  quality: number;
+}
+
+const COMPRESSION_ATTEMPTS: CompressionAttempt[] = [
+  { scale: 1, quality: 0.86 },
+  { scale: 1, quality: 0.74 },
+  { scale: 1, quality: 0.62 },
+  { scale: 1, quality: 0.5 },
+  { scale: 0.85, quality: 0.7 },
+  { scale: 0.7, quality: 0.65 },
+  { scale: 0.55, quality: 0.6 },
+  { scale: 0.4, quality: 0.55 },
+];
+
+export function calculateTargetDimensions(
+  width: number,
+  height: number,
+  maxDimension = MAX_UPLOAD_IMAGE_DIMENSION
+): ImageDimensions {
+  if (
+    !Number.isFinite(width) ||
+    !Number.isFinite(height) ||
+    !Number.isFinite(maxDimension) ||
+    width <= 0 ||
+    height <= 0 ||
+    maxDimension <= 0
+  ) {
+    throw new Error('Image dimensions must be positive finite numbers.');
+  }
+
+  const scale = Math.min(1, maxDimension / Math.max(width, height));
+
+  return {
+    width: Math.max(1, Math.round(width * scale)),
+    height: Math.max(1, Math.round(height * scale)),
+  };
+}
+
+export function shouldCompressImage(
+  fileSize: number,
+  dimensions: ImageDimensions,
+  maxBytes = MAX_UPLOAD_IMAGE_BYTES,
+  maxDimension = MAX_UPLOAD_IMAGE_DIMENSION
+): boolean {
+  return (
+    fileSize > maxBytes ||
+    dimensions.width > maxDimension ||
+    dimensions.height > maxDimension
+  );
+}
+
+export function buildCompressedFileName(fileName: string): string {
+  const extensionIndex = fileName.lastIndexOf('.');
+  const baseName = extensionIndex > 0 ? fileName.slice(0, extensionIndex) : fileName;
+  return `${baseName || 'image'}.${OUTPUT_EXTENSION}`;
+}
+
+function getFileExtension(fileName: string): string {
+  const extensionIndex = fileName.lastIndexOf('.');
+  return extensionIndex >= 0 ? fileName.slice(extensionIndex + 1).toLowerCase() : '';
+}
+
+export function isImageInputFile(file: Pick<File, 'name' | 'type'>): boolean {
+  return file.type.startsWith('image/') || BACKEND_IMAGE_EXTENSIONS.has(getFileExtension(file.name));
+}
+
+export function canUploadOriginalImage(file: Pick<File, 'name' | 'type'>): boolean {
+  const hasAllowedExtension = BACKEND_IMAGE_EXTENSIONS.has(getFileExtension(file.name));
+  const hasAllowedMimeType = file.type === '' || BACKEND_IMAGE_MIME_TYPES.has(file.type.toLowerCase());
+  return hasAllowedExtension && hasAllowedMimeType;
+}
+
+export function canUploadOriginalAfterCompressionFailure(
+  fileSize: number,
+  maxBytes = MAX_FALLBACK_UPLOAD_IMAGE_BYTES
+): boolean {
+  return fileSize <= maxBytes;
+}
+
+function useOriginalOrThrow(file: File, cause: unknown): File {
+  if (!canUploadOriginalImage(file)) {
+    throw new Error(
+      `${file.name} 파일을 지원하는 이미지 형식으로 변환할 수 없습니다. ` +
+        'JPEG, PNG 또는 WebP로 변환한 뒤 다시 시도해주세요.',
+      { cause }
+    );
+  }
+
+  if (!canUploadOriginalAfterCompressionFailure(file.size)) {
+    throw new Error(
+      `${file.name} 파일은 15 MB보다 크고 브라우저에서 크기를 줄일 수 없습니다. ` +
+        'JPEG나 PNG로 변환하거나 더 작은 이미지를 선택해주세요.',
+      { cause }
+    );
+  }
+
+  console.warn(`Image compression was unavailable for ${file.name}; uploading the original.`, cause);
+  return file;
+}
+
+function decodeWithImageElement(file: File): Promise<DecodedImage> {
+  return new Promise((resolve, reject) => {
+    const objectUrl = URL.createObjectURL(file);
+    const image = new Image();
+
+    image.onload = () => {
+      resolve({
+        source: image,
+        width: image.naturalWidth,
+        height: image.naturalHeight,
+        dispose: () => URL.revokeObjectURL(objectUrl),
+      });
+    };
+    image.onerror = () => {
+      URL.revokeObjectURL(objectUrl);
+      reject(new Error(`Unable to decode image: ${file.name}`));
+    };
+    image.src = objectUrl;
+  });
+}
+
+async function decodeImage(file: File): Promise<DecodedImage> {
+  if (typeof createImageBitmap === 'function') {
+    const bitmap = await createImageBitmap(file);
+    return {
+      source: bitmap,
+      width: bitmap.width,
+      height: bitmap.height,
+      dispose: () => bitmap.close(),
+    };
+  }
+
+  return decodeWithImageElement(file);
+}
+
+function canvasToBlob(canvas: HTMLCanvasElement, quality: number): Promise<Blob> {
+  return new Promise((resolve, reject) => {
+    canvas.toBlob(
+      (blob) => {
+        if (blob) {
+          resolve(blob);
+        } else {
+          reject(new Error('The browser could not compress the image.'));
+        }
+      },
+      OUTPUT_MIME_TYPE,
+      quality
+    );
+  });
+}
+
+export async function compressImageForUpload(file: File): Promise<File> {
+  if (!isImageInputFile(file)) {
+    throw new Error(`지원하지 않는 이미지 파일입니다: ${file.name}`);
+  }
+
+  let decoded: DecodedImage;
+  try {
+    decoded = await decodeImage(file);
+  } catch (error) {
+    return useOriginalOrThrow(file, error);
+  }
+
+  try {
+    if (
+      canUploadOriginalImage(file) &&
+      !shouldCompressImage(file.size, {
+        width: decoded.width,
+        height: decoded.height,
+      })
+    ) {
+      return file;
+    }
+
+    const baseDimensions = calculateTargetDimensions(decoded.width, decoded.height);
+    let smallestBlob: Blob | null = null;
+
+    try {
+      const canvas = document.createElement('canvas');
+      const context = canvas.getContext('2d');
+
+      if (!context) {
+        throw new Error('The browser does not support image compression.');
+      }
+
+      for (const attempt of COMPRESSION_ATTEMPTS) {
+        canvas.width = Math.max(1, Math.round(baseDimensions.width * attempt.scale));
+        canvas.height = Math.max(1, Math.round(baseDimensions.height * attempt.scale));
+
+        // JPEG has no alpha channel. A white background avoids transparent pixels
+        // becoming black when PNG/WebP images are converted.
+        context.fillStyle = '#ffffff';
+        context.fillRect(0, 0, canvas.width, canvas.height);
+        context.drawImage(decoded.source, 0, 0, canvas.width, canvas.height);
+
+        const blob = await canvasToBlob(canvas, attempt.quality);
+        if (!smallestBlob || blob.size < smallestBlob.size) {
+          smallestBlob = blob;
+        }
+
+        if (blob.size <= MAX_UPLOAD_IMAGE_BYTES) {
+          return new File([blob], buildCompressedFileName(file.name), {
+            type: blob.type || OUTPUT_MIME_TYPE,
+            lastModified: file.lastModified,
+          });
+        }
+      }
+    } catch (error) {
+      return useOriginalOrThrow(file, error);
+    }
+
+    const measuredSize = smallestBlob?.size ?? file.size;
+    throw new Error(
+      `${file.name} 파일을 ${Math.round(MAX_UPLOAD_IMAGE_BYTES / (1024 * 1024))} MB 이하로 ` +
+        `압축할 수 없습니다(압축 결과: ${Math.ceil(measuredSize / (1024 * 1024))} MB).`
+    );
+  } finally {
+    decoded.dispose();
+  }
+}
diff --git a/src/utils/imageUpload.ts b/src/utils/imageUpload.ts
new file mode 100644
index 0000000..bf0b4a4
--- /dev/null
+++ b/src/utils/imageUpload.ts
@@ -0,0 +1,83 @@
+import type { ImageUploadResponse, ImageUrlItem } from '../types/api';
+import { compressImageForUpload } from './imageCompression.ts';
+
+export const MAX_IMAGES_PER_UPLOAD_TASK = 100;
+
+export type ImageUploadRequest = (formData: FormData) => Promise<ImageUploadResponse>;
+export type ImageCompressor = (file: File) => Promise<File>;
+
+interface ImageUploadFormOptions {
+  imageUrls?: ImageUrlItem[];
+  file?: File;
+  taskId?: string;
+  finalize?: boolean;
+}
+
+export function createImageUploadFormData({
+  imageUrls = [],
+  file,
+  taskId,
+  finalize,
+}: ImageUploadFormOptions): FormData {
+  const formData = new FormData();
+
+  if (imageUrls.length > 0) {
+    formData.append('images_json', JSON.stringify(imageUrls));
+  }
+  if (taskId) {
+    formData.append('task_id', taskId);
+  }
+  if (finalize !== undefined) {
+    formData.append('finalize', String(finalize));
+  }
+  if (file) {
+    formData.append('files', file);
+  }
+
+  return formData;
+}
+
+export async function uploadImagesSequentially(
+  imageUrls: ImageUrlItem[],
+  files: File[],
+  sendRequest: ImageUploadRequest,
+  compressFile: ImageCompressor = compressImageForUpload
+): Promise<ImageUploadResponse> {
+  const totalImageCount = imageUrls.length + files.length;
+  if (totalImageCount > MAX_IMAGES_PER_UPLOAD_TASK) {
+    throw new Error(`이미지는 한 번에 최대 ${MAX_IMAGES_PER_UPLOAD_TASK}장까지 업로드할 수 있습니다.`);
+  }
+
+  if (files.length === 0) {
+    return sendRequest(createImageUploadFormData({ imageUrls }));
+  }
+
+  let taskId: string | undefined;
+  let finalResponse: ImageUploadResponse | undefined;
+
+  for (let index = 0; index < files.length; index += 1) {
+    // Compress and upload one source at a time. This prevents both decoded
+    // image buffers and multipart request bodies from accumulating in memory.
+    const compressedFile = await compressFile(files[index]);
+    const isFirstRequest = index === 0;
+    const isLastRequest = index === files.length - 1;
+    const formData = createImageUploadFormData({
+      imageUrls: isFirstRequest ? imageUrls : [],
+      file: compressedFile,
+      taskId,
+      finalize: isLastRequest,
+    });
+
+    finalResponse = await sendRequest(formData);
+    if (!finalResponse.task_id) {
+      throw new Error('이미지 업로드 응답에 작업 ID가 없습니다.');
+    }
+    if (taskId && finalResponse.task_id !== taskId) {
+      throw new Error('이미지 업로드 작업 ID가 요청 사이에 변경되었습니다. 다시 시도해주세요.');
+    }
+    taskId = finalResponse.task_id;
+  }
+
+  // files.length > 0 guarantees that the loop produced a response.
+  return finalResponse as ImageUploadResponse;
+}