Compare Two Images

About comparing two images

Two files that look the same. One of them is the one the client approved. Something in the other one moved, and nobody wrote down what.

Staring at two pictures side by side is how people miss a two-pixel shift, a colour that changed by one step, or a line of text that quietly got shorter. Your eyes are good at faces and terrible at this.

This tool does the looking for you. Drop both images in and it marks every pixel that differs — or lets you wipe between them, or fade one into the other.

Three views, because one is never enough

• Differences — every pixel that changed, painted in a colour you can't miss, with the unchanged picture dimmed to a grey ghost behind it. This is the view that answers *where*.
• Slider — both images at full quality with a handle you drag across. This is the view that answers *what it actually looks like*. Drag the handle itself or use the Position slider.
• Fade — dissolve from one to the other. This is the one that catches drifts: a whole block nudged down by three pixels fills a difference map with solid colour, but as a fade you see it move.

Start with Differences to find the changes, then switch to Slider to judge them.

The count at the bottom

Under the picture you get the number: what share of the pixels differ, and how many that is. Identical files say so outright, which is often the whole question — did that re-export actually change anything?

Sensitivity controls how much difference counts as a difference. Leave it in the middle for most work. Raise it when JPEG compression noise is lighting up the whole image; lower it to catch a one-step colour change that a screenshot re-encode introduced.

Images of different sizes

If the two images aren't the same size, the second is scaled to match the first so they can be overlaid at all — and the tool says so.

Be careful with the difference map in that case: scaling resamples every pixel, so almost everything will be marked and the map tells you nothing. The slider and the fade are the views to use. To compare properly, make both the same size first with Image Resizer.

Neither image is uploaded

Both are read and compared inside your browser, on your device. Nothing goes to a server.

That matters more than it sounds for this particular tool, because the images people compare are unreleased designs, client work under NDA, internal dashboards, medical or legal scans, and screenshots full of things nobody meant to publish.

What people use it for

• Checking what actually changed between two exports of the same design
• Spotting a visual regression — a screenshot of a page before and after a change
• Comparing a photo before and after editing, to see exactly what an app did
• Checking whether a re-saved or re-compressed file is really identical
• Comparing two scans of the same document for a quiet alteration
• Proofing print artwork against the approved version

Good to know

• Download this view saves whatever is on screen — the difference map, the slider position or the fade — as a PNG you can send to someone
• Swap sides flips which image is which, useful when you loaded them the wrong way round
• A transparent PNG keeps its transparency; the chequerboard behind the picture is the page, not the image
• Very large images (above about 8000 px on a side) may be slow, because every pixel is compared
• This compares the pixels, not the file. Two files with identical pixels but different metadata will read as identical here — use File Checksum if you need to know the bytes match
• For documents rather than pictures, use Compare Two PDFs

How to use it

• Upload the original image on the left and the changed one on the right
• Start on Differences to see where anything moved
• Adjust Sensitivity if compression noise is drowning the real changes
• Switch to Slider or Fade to judge what the change actually looks like
• Press Download this view if you need to send the result on

Related tools

• Compare Two PDFs — the same idea, for documents
• Text Diff — compare two pieces of text
• Compare Two Folders — which files differ across whole folders
• Image Resizer — make both images the same size first
• File Checksum — check whether two files are byte-for-byte identical
• Image Metadata — see what is hidden inside each file