Image Diff & Compare
Drop two images and spot the differences: slider overlay, side-by-side, and pixel-diff heatmap with a change-percentage score.
How image comparison works: pixel diff, explained
Image comparison at its simplest: subtract pixel A from pixel B, take the absolute value, and you get a per-pixel difference map. Average that map and you get a difference score, a single number telling you how much two images differ. Zero means byte-identical. 1.0 means maximum possible difference (white vs black). Most real-world compares land between 0.001 (same image saved twice) and 0.3 (substantively different images).
This tool compares the images at image A's own resolution, fitting a differently sized image B inside it without stretching. It then produces three views: a drag-to-reveal slider, a side-by-side grid, and a heatmap showing exactly where pixels differ. Used daily for design QA, client-revision review, photo-edit detection, and A/B visual testing.
If your diff shows changes and you want to know what kind of edit was applied, check the file's metadata with our Metadata Viewer: the EXIF Software field usually names the editor (Photoshop, Lightroom, Snapseed, etc.). For sharpness changes specifically, pair the diff with the AI Image Sharpener to see if one version has been sharpened relative to the other.
What people compare images for
QA a design revision from a client
Client sent back a design mockup with "small tweaks". Drop the original and the revision; diff mode highlights exactly what changed. Great for spotting accidental edits, confirming only the requested areas were touched, and sign-off documentation.
Spot differences between two photos
Two versions of the same scene (before/after retouching, two security- camera frames, product photography with/without reflection removal), the heatmap shows every pixel-level change. Faster than blinking two Photoshop layers on and off.
Verify if a photo has been edited
Got a suspicious image and the original? Diff mode shows where modifications were made: cloned objects leave halo patterns, colour adjustments produce wide faint regions, skin retouching shows concentrated edits around faces. For additional forensic signals, check file metadata with the Metadata Viewer.
Compare compression quality
Testing JPEG quality 80 vs 90 vs 95? WebP vs AVIF at matched file sizes? Drop the output of each compression setting against the original. The score quantifies the quality loss; the heatmap shows where artefacts concentrate (usually sharp edges and areas of fine detail).
Verify AI upscaling or sharpening output
Compare the input and output of any image-processing step to quantify change. Particularly useful for evaluating AI tools: compare the source to the AI Image Upscaler output to see the edge changes; compare sharpened vs unsharpened to see where the sharpener acted.
Design-system visual regression testing
Engineers verifying a CSS change didn't break other parts of the UI drop pre-change and post-change screenshots. Diff mode confirms the only visual changes are where the engineer intended them to be. Free alternative to paid visual-regression SaaS tools for small teams.
When to use slider, side-by-side, or diff
Subtle differences
Drag-to-reveal overlay. Best when the differences are small and you want to direct your eye to specific spots. Great for client revisions where 'look at the button area' is the workflow.
Full context at once
Both images visible in parallel at the same time. Best when you need to see the full composition of each without switching back and forth. Ideal for design reviews.
Exhaustive change audit
Every changed pixel is highlighted, blue for slight and red for large. Best when you need to find ALL differences: compression QA, edit detection, regression testing. Combine with the numerical score for a summary.
Four steps, no signup
Upload two images
Drop the 'before' version and the 'after' version: JPG, PNG, or WEBP up to 10MB each. Different sizes are fine: image B is fitted inside image A at A's own resolution, and only the area they share is compared. Nothing is uploaded.
Pick a view mode
Slider reveals one image over the other at your cursor position. Side-by-side shows both at full size in parallel. Diff mode shows a heatmap of every pixel where the two images differ, coloured from blue (slight) to red (large).
Read the difference score
The percentage of pixels that changed noticeably. Under 1% usually means the same image saved twice; a few percent is typical of compression or format changes; well above 10% means substantive edits.
Inspect the heatmap
Diff mode shows exactly where the images differ: text changes glow bright, retouched regions show halos, compression artefacts produce fine speckle. Great for QA on client revisions and design iterations.
Three view modes, one score, zero uploads
Most online diff tools upload your files and give you one view mode. Ours runs instantly, with three view modes and a numerical change score.
Private
Neither file is uploaded. No upload, no retention. Works for confidential client work and sensitive internal comparisons.
Numerical + visual
A single change score (the percentage of pixels that differ) plus a pixel-level heatmap. Summary number for reports, detailed view for investigation.
Any resolution, any aspect
Image B is fitted inside image A without stretching, and only the area they share is scored. Practical for comparing a thumbnail against a full-size original.
Free, unlimited, commercial use
Compare as many pairs as you need per day. No account, no watermark on the heatmap PNG, no usage restrictions.
Frequently asked
Q.What does the difference score mean?
Q.Why are two identical-looking images showing a non-zero score?
Q.Can this detect if a photo has been edited?
Q.Does size or aspect ratio need to match?
Q.What's the difference between this and Photoshop's 'Difference' layer blend mode?
Q.Is this really free? Are my images uploaded?
Q.Can I use the diff heatmap commercially?
Q.What file types work best?
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