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Base64 Image Decoder

Image

Convert base64 encoded strings back to downloadable images

Base64 String Input

Decoded Image

Decoded image will appear here...

How to Use

This tool decodes base64 encoded images back to their original format.

Supported formats:

  • Full data URI: data:image/png;base64,iVBORw0...
  • Base64 string only: iVBORw0KGgo...

Tip: You can paste the output from our Base64 Image Encoder tool directly!

Deep Dive: Base64 Image Decoder

Published 2024-01-01T08:00:00+08:00
Last updated 2025-12-30T13:45:00+05:00

Base64 decoding converts encoded ASCII text strings back to binary image data. Paste a data URI or raw base64 string, and this tool extracts the image in its original format (PNG, JPG, WebP, GIF). All processing happens in your browser for complete privacy.

Privacy Architecture

This tool uses client-side WebAssembly to ensure your data never touches a server. Secure, fast, and 100% private by design.

Secure Engine Active

Core Capabilities

  • Decode base64 to image
  • Supports data URI format
  • Accepts raw base64 strings
  • Auto-detects image format
  • Download decoded image
  • Preview before download
  • Shows image size info
  • 100% Client-side processing

Why It Matters

  • Extract: Get images embedded in HTML/CSS back
  • Download: Save base64 images from emails or code
  • Verify: Check what an encoded string contains
  • Convert: Get usable image files from base64
  • Privacy: No server uploads—all local processing

Quick Start Guide

01

Paste base64 string (with or without data URI prefix)

02

Click 'Decode to Image'

03

Preview the decoded image

04

Download in original format (PNG, JPG, etc.)

05

Clear and decode another!

Usage Examples

Data URI Format

Scenario 01

Decode complete data URI

Input
data:image/png;base64,iVBORw0KGgo...
Output
decoded-image.png (downloadable)

Raw Base64

Scenario 02

Decode without data URI prefix

Input
iVBORw0KGgoAAAANSUhEU...
Output
decoded-image.png (default PNG format)

From Email

Scenario 03

Extract embedded email logo

Input
<img src="data:image/jpeg;base64,/9j/4AAQ...">
Output
logo.jpeg - downloaded and usable!

Common Scenarios

Extract Email Images

Get images embedded in HTML emails

Step 1Step 2Step 3Step 4Step 5

Debug Web Code

Check what base64 string contains

Step 1Step 2Step 3Step 4Step 5

Questions?

Technical Architecture

How Base64 Decoding Works

Base64 represents binary data using 64 ASCII characters (A-Z, a-z, 0-9, +, /). Decoding reverses this: every 4 Base64 characters are converted back into 3 bytes of binary data. The tool strips metadata headers (like `data:image/png;base64,`) and parses the remaining string. Padding characters (`=`) at the end indicate the byte alignment. Browser's `atob()` function or `Buffer` (in Node) handles this conversion, turning the string back into a Blob (Binary Large Object) representing the original image file.

MIME Types and Data URIs

**Data URI Scheme**: `data:[<media type>][;base64],<data>` - **Media Type**: Tells the browser what file it is (e.g., `image/png`, `image/jpeg`). - **Base64**: The encoding method. - **Data**: The actual encoded string. Our decoder looks for this media type in the header to set the correct file extension for download. If missing, we analyze the binary signature (magic numbers) to guess: `89 50 4E 47` = PNG, `FF D8 FF` = JPEG.

Base64 Efficiency

**Size Increase**: Base64 encoded images are roughly 33% larger than the original binary file. This is because 3 bytes (24 bits) are represented by 4 characters (32 bits). **Performance**: Decoding strictly large Base64 strings (10MB+) on the client side can freeze the main thread. We use optimized Blob handling to minimize memory impact, but extremely large strings might still cause browser lag.

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