Three ways to answer "what changed between these two images?": a before/after slider for visual sweeps, an onion-skin overlay for alignment checks, and a true pixel diff that marks every changed pixel magenta over a dimmed grayscale base — with the changed percentage, exact pixel count, and bounding regions. The adjustable threshold separates real edits from invisible JPEG re-compression noise, so "identical" actually means identical.
Both images stay on your device — the entire comparison runs in your browser, HEIC photos included. Comparing text or code instead of pixels? Use the text diff or JSON diff. And if the images differ only in size, the image resizer can normalize them first.
Frequently asked questions
How do I compare two images online?
Drop both images into the tool and pick a view: Slider overlays them with a draggable divider (perfect for before/after edits), Onion skin blends them with an opacity control (great for spotting alignment shifts), and Diff computes a pixel-by-pixel comparison that paints every changed pixel magenta over a dimmed grayscale base, with exact change statistics.
What does the threshold slider do?
It sets how different a pixel must be before it counts as changed — the per-channel color distance from 0 to 128. A low threshold flags even one-step color shifts (including invisible ones from JPEG re-compression); around 25 ignores compression noise while catching real edits; higher values only flag strong changes. Slide it and watch the magenta regions react live.
Can I compare images of different sizes?
Yes. By default the tool compares the overlapping top-left region and tells you the sizes differ — the honest comparison when one image is a crop of the other. The diff engine can also stretch the second image to match the first, which suits comparing the same photo exported at two resolutions.
What is an image diff useful for?
Spot-the-difference on real work: verifying what a designer changed between two mockup exports, checking whether a photo was retouched, catching visual regressions between two screenshots of your app, or confirming that two seemingly identical files really are identical (0.00% changed).
Are my images uploaded?
No — both images are read and compared entirely in your browser, including the pixel-level diff. Nothing is sent to a server, so it is safe to compare private screenshots or unreleased design work. iPhone HEIC photos work too.