How to Tell if Two Images Are Different
Two files can look exactly the same on screen and still not be the same image. One may be a re-saved copy, a lightly edited version, or a file with a small change you cannot spot by eye. Here are the main ways to compare them, from quickest to most exact.
1. Side by side
Open both images at the same size and flick between them. This catches big changes: a removed object, a new crop, a colour shift. It misses small ones.
2. Overlay with a slider
Put one image on top of the other and drag a slider across. Edges that jump or shift show where something changed. This is good for spotting retouching on faces or products.
3. Pixel difference
A difference view subtracts one image from the other. Pixels that match turn black. Pixels that differ light up. Even a change of a few pixels becomes easy to see.
magick compare a.png b.png diff.png, and can also print a number that says how different the two files are.4. Compare the file data
Images also carry hidden details: camera model, date taken, editing app, and sometimes a label that says AI was used. Two images with the same pixels can have very different file data. Checking it tells you which copy is the original and which was edited or exported later.
When each method helps
- Checking a client's edits: slider overlay.
- Finding a tiny change, like a removed watermark: pixel difference.
- Finding duplicates in a folder: pixel difference plus file size.
- Working out which file is the original: compare the file data.
A quick way to do it online
If you do not want to install anything, you can compare two images in the browser, with a slider and a difference view, without uploading them to a server.