diff --git a/CHANGELOG.md b/CHANGELOG.md
index 3aaa4524da21c59703d8f641606cd8934d497ed1..13102ef7dd1b8dad05757066af8e418d43a3ccf7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -20,7 +20,8 @@ You should also include the user name that made the change.
 - enhance(client): DM作成時にメンションも含むように
 - enhance(client): フォロー申請のボタンのデザインを改善
 - enhance(backend): OpenAPIエンドポイントを復旧
-- 透明なWebP/AVIF映像はJPEGではなくWebPに変換するように
+- WebP/AVIF/JPEGのweb公開用画像は、サーバーサイドではJPEGではなくWebPに変換するように
+- アニメーション画像のサムネイルを生成するように
 - アクティブユーザー数チャートの記録上限値を拡張
 - Playのソースコード上限文字数を2倍に拡張
 - 付箋ウィジェットの高さを設定可能に
diff --git a/packages/backend/src/core/DriveService.ts b/packages/backend/src/core/DriveService.ts
index 7eccf4b3b1fc36fda0ed3982b7ddf2673db1e434..f1e93d6dd9d5019b341c373dedf2a98ac68c6551 100644
--- a/packages/backend/src/core/DriveService.ts
+++ b/packages/backend/src/core/DriveService.ts
@@ -295,7 +295,7 @@ export class DriveService {
 
 			satisfyWebpublic = !!(
 				type !== 'image/svg+xml' && // security reason
-				type !== 'image/avif' && // not supported by Mastodon
+				type !== 'image/avif' && // not supported by Mastodon and MS Edge
 			!(metadata.exif ?? metadata.iptc ?? metadata.xmp ?? metadata.tifftagPhotoshop) &&
 			metadata.width && metadata.width <= 2048 &&
 			metadata.height && metadata.height <= 2048
@@ -339,7 +339,7 @@ export class DriveService {
 			if (isAnimated) {
 				thumbnail = await this.imageProcessingService.convertSharpToWebp(sharp(path, { animated: true }), 374, 317, { alphaQuality: 70 });
 			} else {
-				thumbnail = await this.imageProcessingService.convertSharpToAvif(img, 498, 422);
+				thumbnail = await this.imageProcessingService.convertSharpToWebp(img, 498, 422);
 			}
 		} catch (err) {
 			this.registerLogger.warn('thumbnail not created (an error occured)', err as Error);
diff --git a/packages/backend/src/core/entities/DriveFileEntityService.ts b/packages/backend/src/core/entities/DriveFileEntityService.ts
index 1a6913b800cd26aeae1c73fbe5437ddd9cd6ed06..2d40f444cb4ee5cbcbd09eb59f4467c7560674dc 100644
--- a/packages/backend/src/core/entities/DriveFileEntityService.ts
+++ b/packages/backend/src/core/entities/DriveFileEntityService.ts
@@ -76,7 +76,7 @@ export class DriveFileEntityService {
 	@bindThis
 	private getProxiedUrl(url: string, mode?: 'static' | 'avatar'): string {
 		return appendQuery(
-			`${this.config.mediaProxy}/${mode ?? 'image'}.${mode === 'avatar' ? 'webp' : 'avif'}`,
+			`${this.config.mediaProxy}/${mode ?? 'image'}.webp`,
 			query({
 				url,
 				...(mode ? { [mode]: '1' } : {}),
diff --git a/packages/backend/src/server/FileServerService.ts b/packages/backend/src/server/FileServerService.ts
index fb1c67f20d43514017d514ad58dc2b0b2bf0f595..794fa76d9e5cb92ed8fb4dabda4c80e49ec7e484 100644
--- a/packages/backend/src/server/FileServerService.ts
+++ b/packages/backend/src/server/FileServerService.ts
@@ -130,7 +130,7 @@ export class FileServerService {
 					if (isMimeImage(file.mime, 'sharp-convertible-image-with-bmp')) {
 						reply.header('Cache-Control', 'max-age=31536000, immutable');
 
-						const url = new URL(`${this.config.mediaProxy}/static.avif`);
+						const url = new URL(`${this.config.mediaProxy}/static.webp`);
 						url.searchParams.set('url', file.url);
 						url.searchParams.set('static', '1');
 
@@ -151,7 +151,7 @@ export class FileServerService {
 					if (['image/svg+xml'].includes(file.mime)) {
 						reply.header('Cache-Control', 'max-age=31536000, immutable');
 
-						const url = new URL(`${this.config.mediaProxy}/svg.avif`);
+						const url = new URL(`${this.config.mediaProxy}/svg.webp`);
 						url.searchParams.set('url', file.url);
 
 						file.cleanup();
@@ -291,9 +291,9 @@ export class FileServerService {
 					};
 				}
 			} else if ('static' in request.query) {
-				image = this.imageProcessingService.convertSharpToAvifStream(await sharpBmp(file.path, file.mime), 498, 422);
+				image = this.imageProcessingService.convertSharpToWebpStream(await sharpBmp(file.path, file.mime), 498, 422);
 			} else if ('preview' in request.query) {
-				image = this.imageProcessingService.convertSharpToAvifStream(await sharpBmp(file.path, file.mime), 200, 200);
+				image = this.imageProcessingService.convertSharpToWebpStream(await sharpBmp(file.path, file.mime), 200, 200);
 			} else if ('badge' in request.query) {
 				const mask = (await sharpBmp(file.path, file.mime))
 					.resize(96, 96, {
@@ -325,7 +325,7 @@ export class FileServerService {
 					type: 'image/png',
 				};
 			} else if (file.mime === 'image/svg+xml') {
-				image = this.imageProcessingService.convertToAvifStream(file.path, 2048, 2048);
+				image = this.imageProcessingService.convertToWebpStream(file.path, 2048, 2048);
 			} else if (!file.mime.startsWith('image/') || !FILE_TYPE_BROWSERSAFE.includes(file.mime)) {
 				throw new StatusError('Rejected type', 403, 'Rejected type');
 			}
diff --git a/packages/backend/src/server/web/UrlPreviewService.ts b/packages/backend/src/server/web/UrlPreviewService.ts
index 5f4d53d0ec55aa7c0e110b51657269baf00c9c97..2ce7293a529a2883decdbddcf09631d838d17b37 100644
--- a/packages/backend/src/server/web/UrlPreviewService.ts
+++ b/packages/backend/src/server/web/UrlPreviewService.ts
@@ -33,7 +33,7 @@ export class UrlPreviewService {
 	private wrap(url?: string | null): string | null {
 		return url != null
 			? url.match(/^https?:\/\//)
-				? `${this.config.mediaProxy}/preview.avif?${query({
+				? `${this.config.mediaProxy}/preview.webp?${query({
 					url,
 					preview: '1',
 				})}`
diff --git a/packages/frontend/src/scripts/media-proxy.ts b/packages/frontend/src/scripts/media-proxy.ts
index d0c95e0b75cec8ae4e25857c0ee0f8431410af1d..91ac14c06d3a4c0508678b472f03093bde3a4f03 100644
--- a/packages/frontend/src/scripts/media-proxy.ts
+++ b/packages/frontend/src/scripts/media-proxy.ts
@@ -11,7 +11,7 @@ export function getProxiedImageUrl(imageUrl: string, type?: 'preview', mustOrigi
 	}
 
 	return `${mustOrigin ? localProxy : instance.mediaProxy}/${
-		type === 'preview' ? 'preview.avif'
+		type === 'preview' ? 'preview.webp'
 		: 'image.webp'
 	}?${query({
 		url: imageUrl,
@@ -41,7 +41,7 @@ export function getStaticImageUrl(baseUrl: string): string {
 		return u.href;
 	}
 
-	return `${instance.mediaProxy}/static.avif?${query({
+	return `${instance.mediaProxy}/static.webp?${query({
 		url: u.href,
 		static: '1',
 	})}`;