Image Diff Checker
Free online image diff tool. Runs entirely in your browser - no upload.
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What is Image Diff Checker?
Image Diff Checker is a free browser-based tool that compares two images pixel by pixel. It highlights every changed pixel in red over a dimmed grayscale base, reports the changed-pixel percentage, and offers side-by-side, difference, and heat-map views with an adjustable threshold - all processed locally with no upload.
Key Benefits
- Catch visual regressions in UI screenshots before shipping
- 100% private - images never leave your browser
- Objective similarity verdict via changed-pixel percentage
- Threshold control separates real changes from compression noise
- Exportable PNG diff for bug reports, pull requests, and design reviews
Common Use Cases
- •QA teams comparing a fresh build screenshot against a known-good baseline
- •Developers verifying that a CSS refactor changed nothing visually
- •Designers reviewing handoff files against the implemented result
- •Photographers and editors checking the effect of a re-encode or filter
- •Content teams spotting unwanted changes in updated banner artwork
How to Compare Two Images
- Upload both images: Click the Before and After slots to pick the original and modified images from your device. Files stay local - nothing is uploaded.
- Choose a view mode: Pick Difference to overlay changes in red, Heat Map to see change intensity, or Side by Side for a manual visual check.
- Tune the threshold: Raise the threshold slider to ignore invisible noise like anti-aliasing and JPEG artifacts; lower it to catch the subtlest edits.
- Read the stats and export: Check the changed-pixel count and difference percentage for an objective verdict, then download the diff as a PNG to share it.
Key Features
- Pixel-by-pixel comparison that flags every changed pixel in red
- Adjustable 0-255 threshold to filter anti-aliasing and compression noise
- Side-by-side, difference, and intensity heat-map view modes
- Changed-pixel count and difference percentage with instant verdict
- Download the diff as a PNG for bug reports and pull requests
Frequently Asked Questions
Are my images uploaded to a server?
No. Both images are decoded and compared on an HTML canvas inside your browser. Nothing leaves your device, so the tool is safe for confidential screenshots and designs.
What does the threshold slider do?
Each pixel gets a difference score from 0 to 255 (the largest per-channel gap). Pixels scoring at or below the threshold count as unchanged. Raising it hides invisible noise; lowering it surfaces subtle edits.
Can I compare images with different sizes?
Yes. Both images are scaled to the largest shared dimensions before comparing, so alignment is preserved. For pixel-accurate results, compare images of identical size.
What image formats are supported?
JPEG, PNG, WebP, GIF, and BMP - any format your browser can decode. The result can be downloaded as a PNG with changes highlighted in red.