diff --git a/CHANGELOG.md b/CHANGELOG.md
index e57a2c4fd3..685a15f4e0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -33,6 +33,9 @@
 - Enhance: AiScriptで`LOCALE`として現在の設定言語を取得できるように
 - `$[rainbow ]`記法が、動きのあるMFMが無効になっていても使用できるようになりました
 - Playの操作を行うAPI TokenをAPIコンソールから発行できるように
+- 画像の圧縮方法を選択可能にしました
+    - サイズ変更を行うかを選択可能にしました
+    - 強制的に非可逆圧縮できるようになりました
 - Fix: サーバー情報画面(`/instance-info/{domain}`)でブロックができないのを修正
 - Fix: 未読のお知らせの「わかった」をクリック・タップしてもその場で「わかった」が消えない問題を修正
 - Fix: iOSで画面を回転させるとテキストサイズが変わる問題を修正
diff --git a/locales/index.d.ts b/locales/index.d.ts
index 1f25edd0ef..5e996bf2bd 100644
--- a/locales/index.d.ts
+++ b/locales/index.d.ts
@@ -2202,6 +2202,14 @@ export interface Locale {
             "mention": string;
         };
     };
+    "_imageCompressionMode": {
+        "title": string;
+        "description": string;
+        "resizeCompress": string;
+        "noResizeCompress": string;
+        "resizeCompressLossy": string;
+        "noResizeCompressLossy": string;
+    };
 }
 declare const locales: {
     [lang: string]: Locale;
diff --git a/locales/ja-JP.yml b/locales/ja-JP.yml
index 2e0e64bbef..c66353fcf6 100644
--- a/locales/ja-JP.yml
+++ b/locales/ja-JP.yml
@@ -2115,3 +2115,11 @@ _webhookSettings:
     renote: "Renoteされたとき"
     reaction: "リアクションがあったとき"
     mention: "メンションされたとき"
+
+_imageCompressionMode:
+  title: "画像の圧縮形式"
+  description: "オリジナル画像を保持しない場合に、Web公開用画像の圧縮形式を選択できます。縮小する場合は2048x2048より小さくなるように縮小されます。非可逆圧縮を指定しない場合は、元画像に応じて非可逆圧縮か可逆圧縮かが自動的に選択されます。"
+  resizeCompress: "縮小して再圧縮する"
+  noResizeCompress: "縮小せず再圧縮する"
+  resizeCompressLossy: "縮小して非可逆圧縮する"
+  noResizeCompressLossy: "縮小せず非可逆圧縮する"
diff --git a/packages/frontend/src/pages/settings/drive.vue b/packages/frontend/src/pages/settings/drive.vue
index de502e8511..a3ce52232c 100644
--- a/packages/frontend/src/pages/settings/drive.vue
+++ b/packages/frontend/src/pages/settings/drive.vue
@@ -44,6 +44,14 @@ SPDX-License-Identifier: AGPL-3.0-only
 				<template #label>{{ i18n.ts.keepOriginalUploading }}</template>
 				<template #caption>{{ i18n.ts.keepOriginalUploadingDescription }}</template>
 			</MkSwitch>
+			<MkSelect v-model="imageCompressionMode">
+				<template #label>{{ i18n.ts._imageCompressionMode.title }}</template>
+				<option value="resizeCompress">{{ i18n.ts._imageCompressionMode.resizeCompress }}</option>
+				<option value="noResizeCompress">{{ i18n.ts._imageCompressionMode.noResizeCompress }}</option>
+				<option value="resizeCompressLossy">{{ i18n.ts._imageCompressionMode.resizeCompressLossy }}</option>
+				<option value="noResizeCompressLossy">{{ i18n.ts._imageCompressionMode.noResizeCompressLossy }}</option>
+				<template #caption>{{ i18n.ts._imageCompressionMode.description }}</template>
+			</MkSelect>
 			<MkSwitch v-model="alwaysMarkNsfw" @update:modelValue="saveProfile()">
 				<template #label>{{ i18n.ts.alwaysMarkSensitive }}</template>
 			</MkSwitch>
@@ -71,6 +79,7 @@ import MkChart from '@/components/MkChart.vue';
 import { i18n } from '@/i18n';
 import { definePageMetadata } from '@/scripts/page-metadata';
 import { $i } from '@/account';
+import MkSelect from '@/components/MkSelect.vue';
 
 const fetching = ref(true);
 const usage = ref<any>(null);
@@ -91,6 +100,7 @@ const meterStyle = computed(() => {
 });
 
 const keepOriginalUploading = computed(defaultStore.makeGetterSetter('keepOriginalUploading'));
+const imageCompressionMode = computed(defaultStore.makeGetterSetter('imageCompressionMode'));
 
 os.api('drive').then(info => {
 	capacity.value = info.capacity;
diff --git a/packages/frontend/src/scripts/upload/compress-config.ts b/packages/frontend/src/scripts/upload/compress-config.ts
index 8fe64c8b76..a22c259d27 100644
--- a/packages/frontend/src/scripts/upload/compress-config.ts
+++ b/packages/frontend/src/scripts/upload/compress-config.ts
@@ -6,31 +6,105 @@
 import isAnimated from 'is-file-animated';
 import { isWebpSupported } from './isWebpSupported';
 import type { BrowserImageResizerConfig } from 'browser-image-resizer';
+import { defaultStore } from '@/store';
 
 const compressTypeMap = {
-	'image/jpeg': { quality: 0.90, mimeType: 'image/webp' },
-	'image/png': { quality: 1, mimeType: 'image/webp' },
-	'image/webp': { quality: 0.90, mimeType: 'image/webp' },
-	'image/svg+xml': { quality: 1, mimeType: 'image/webp' },
+	'lossy': { quality: 0.90, mimeType: 'image/webp' },
+	'lossless': { quality: 1, mimeType: 'image/webp' },
 } as const;
 
 const compressTypeMapFallback = {
-	'image/jpeg': { quality: 0.85, mimeType: 'image/jpeg' },
-	'image/png': { quality: 1, mimeType: 'image/png' },
-	'image/webp': { quality: 0.85, mimeType: 'image/jpeg' },
-	'image/svg+xml': { quality: 1, mimeType: 'image/png' },
+	'lossy': { quality: 0.85, mimeType: 'image/jpeg' },
+	'lossless': { quality: 1, mimeType: 'image/png' },
 } as const;
 
+const inputCompressKindMap = {
+	'image/jpeg': 'lossy',
+	'image/png': 'lossless',
+	'image/webp': 'lossy',
+	'image/svg+xml': 'lossless',
+} as const;
+
+const resizeSizeConfig = { maxWidth: 2048, maxHeight: 2048 } as const;
+const noResizeSizeConfig = { maxWidth: Number.MAX_SAFE_INTEGER, maxHeight: Number.MAX_SAFE_INTEGER } as const;
+
+async function isLosslessWebp(file: Blob): Promise<boolean> {
+	// file header
+	//   'RIFF': u32 @ 0x00
+	//   file size: u32 @ 0x04
+	//   'WEBP': u32 @ 0x08
+	// for simple lossless
+	//   'VP8L': u32 @ 0x0C
+	// so read 16 bytes and check those three magic numbers
+	const buffer = new Uint8Array(await file.slice(0, 16).arrayBuffer());
+
+	const header = 'RIFF\x00\x00\x00\x00WEBPVP8L';
+	for (let i = 0; i < header.length; i++) {
+		const code = header.charCodeAt(i);
+		if (code === 0) continue;
+		if (buffer[i] !== code) return false;
+	}
+	return true;
+}
+
+async function inputImageKind(file: File): Promise<'lossy' | 'lossless' | undefined> {
+	let compressKind: 'lossy' | 'lossless' | undefined = inputCompressKindMap[file.type];
+	if (!compressKind) return undefined; // unknown image format
+	if (await isAnimated(file)) return undefined; // animated image format
+	// WEBPs can be lossless
+	if (await isLosslessWebp(file)) compressKind = 'lossless';
+	return compressKind;
+}
+
 export async function getCompressionConfig(file: File): Promise<BrowserImageResizerConfig | undefined> {
-	const imgConfig = (isWebpSupported() ? compressTypeMap : compressTypeMapFallback)[file.type];
-	if (!imgConfig || await isAnimated(file)) {
-		return;
+	const inputCompressKind = await inputImageKind(file);
+	if (!inputCompressKind) return undefined;
+
+	let compressKind: 'lossy' | 'lossless';
+	let resize: boolean;
+
+	switch (defaultStore.state.imageCompressionMode) {
+		case 'resizeCompress':
+		case null:
+		default:
+			resize = true;
+			compressKind = inputCompressKind;
+			break;
+		case 'noResizeCompress':
+			resize = false;
+			compressKind = inputCompressKind;
+			break;
+		case 'resizeCompressLossy':
+			resize = true;
+			compressKind = 'lossy';
+			break;
+		case 'noResizeCompressLossy':
+			resize = false;
+			compressKind = 'lossy';
+			break;
+	}
+
+	const webpSupported = isWebpSupported();
+
+	const imgFormatConfig = (webpSupported ? compressTypeMap : compressTypeMapFallback)[compressKind];
+	const sizeConfig = resize ? resizeSizeConfig : noResizeSizeConfig;
+
+	if (!resize) {
+		// we don't resize images so we may omit recompression
+		if (imgFormatConfig.mimeType === file.type && inputCompressKind === compressKind) {
+			// we don't have to recompress already compressed to preferred image format.
+			return undefined;
+		}
+
+		if (!webpSupported && file.type === 'image/webp' && compressKind === 'lossless') {
+			// lossless webp -> png recompression likely to increase image size so don't recompress
+			return undefined;
+		}
 	}
 
 	return {
-		maxWidth: 2048,
-		maxHeight: 2048,
 		debug: true,
-		...imgConfig,
+		...imgFormatConfig,
+		...sizeConfig,
 	};
 }
diff --git a/packages/frontend/src/store.ts b/packages/frontend/src/store.ts
index e9f672384e..bf8cc560cd 100644
--- a/packages/frontend/src/store.ts
+++ b/packages/frontend/src/store.ts
@@ -87,6 +87,10 @@ export const defaultStore = markRaw(new Storage('base', {
 		where: 'account',
 		default: false,
 	},
+	imageCompressionMode: {
+		where: 'account',
+		default: 'resizeCompress' as 'resizeCompress' | 'noResizeCompress' | 'resizeCompressLossy' | 'noResizeCompressLossy' | null,
+	},
 	memo: {
 		where: 'account',
 		default: null,