About the Image Diff Checker
Sometimes two pictures look the same but are not: a screenshot before and after a change, a design and its export, a photo and an edited copy. This tool compares them pixel by pixel and shows you what is different. Pick picture A and picture B, and it paints every changed pixel in red over a faded copy of the original, tells you how many pixels changed and what percentage that is, and gives the size and position of the box that contains all the changes. A sensitivity slider lets you ignore tiny colour differences caused by compression. You can download the difference picture as a PNG. Both pictures are compared in your browser and are never uploaded.
Updated October 2026
How to use the Image Diff Checker
- 1Pick picture A, the original.
- 2Pick picture B, the changed one.
- 3Adjust the sensitivity slider if there is too much or too little red.
- 4Read the number and percentage of changed pixels.
- 5Download the difference picture if you want to share it.
Choosing the sensitivity
At 0, any difference at all counts, even a change of one level in one colour channel. That is right for lossless files such as PNG exports, where an identical result means an identical picture. For photos and JPEG files, set a value around 10 to 30 so that compression noise does not flood the result.
If the red areas are speckled across the whole picture, the sensitivity is too low. If you can see a change with your eyes but the tool shows nothing, the sensitivity is too high or the change is very small.
Good uses
- Check a design export against the original design.
- See what a retouch actually changed.
- Compare two screenshots after a software update.
- Test whether re-saving or compressing changed a picture.
- Find hidden changes in a scanned form or a map.
- Play spot the difference with two similar drawings.
Related tools
For text instead of pictures, use the Diff Checker, and to compare documents use Compare PDFs. Make the pictures the same size first with the Image Resizer or crop them with Crop Image. If you need to rotate one, the Rotate & Flip Image tool helps. Match settings between both pictures to avoid false differences.
Features
- Pixel-by-pixel comparison
- Differences marked in red
- Sensitivity slider to ignore compression noise
- Count, percentage and bounding box of changes
- Handles different sizes by stretching B to A
- Download the difference picture
- Private, no upload
Frequently asked questions
How does the comparison work?
Both pictures are placed on the same size canvas. For each pixel, the biggest difference in red, green, blue and transparency is measured. If it is above your sensitivity setting, the pixel is marked as changed.
Why do I see changes in two pictures that look identical?
JPEG compression and colour profile changes alter many pixels by small amounts. Raise the sensitivity slider to 15 or 25 to hide such noise.
What if the pictures have different sizes?
Picture B is stretched to the size of picture A, and the tool warns you. Comparisons are most reliable when the sizes match exactly.
What does the bounding box mean?
It is the smallest rectangle that contains every changed pixel. It tells you where the changes are and how big the affected area is.
Can I use it to compare screenshots of a website?
Yes. It is useful to check that a change only affected the area you intended. Take both screenshots at the same window size.
Is there a size limit?
Large pictures are scaled down to about 1600 pixels on the longest side for the comparison, which keeps the page fast.
Are my pictures uploaded?
No. They are compared in your browser.