Compare Images — Slider, Pixel Diff & Similarity Score
Compare two images online: drag the before/after slider, highlight pixel-level differences in red, and get PSNR / SSIM similarity scores. Mismatched sizes are aligned automatically; large images are processed in chunks without freezing. Compared locally in your browser — no upload. Works on desktop, tablet & mobile.
Spotting differences between two images by eye is unreliable. This tool gives you two modes: Slider overlays both images with a draggable divider for intuitive before/after comparison — great for design revisions or photo edits; Diff compares the images pixel by pixel, paints every changed region red, and reports three metrics — changed-pixel percentage, PSNR (peak signal-to-noise ratio, higher = closer) and SSIM (structural similarity, 1 = identical). If the two images differ in size, the second is scaled to match the first before comparison. Everything is computed locally in your browser; your images are never uploaded.
When you need this
UI & design review
Two screenshots before/after a change — red highlights find every edit.
Compression quality
Quantify quality loss with PSNR / SSIM after compressing.
Spot the difference
Two seemingly identical images — verify pixel by pixel.
Which mode to use
- Visual before/after: drag the divider for direct comparison
- Ideal for photo edits and design revisions
- Zero computation — drag and see
- Pixel-by-pixel comparison with red highlighted differences
- Three metrics: changed %, PSNR and SSIM
- Large images are processed in async chunks so the page stays responsive
Image comparison FAQ
PSNR measures pixel error in dB — higher is closer, above 40dB differences are usually invisible, identical images score ∞. SSIM models human perception via structure, luminance and contrast — 1 means identical, above 0.99 is virtually indistinguishable. Read them together for a reliable verdict.
Yes. The second image is scaled to match the first before comparison, and the page tells you when this happens. Note that scaling itself introduces small pixel differences — in that case trust SSIM and the highlighted regions more than the raw changed-pixel count.
Usually lossy compression: re-saving as JPG changes pixel values slightly even when nothing is visible. The tool uses a noise threshold so tiny encoding jitter is not flagged; if changed % is tiny and PSNR is high, it is almost certainly just encoding noise.
No. Both the slider view and the pixel diff run entirely in your browser. Images are never uploaded or stored, and the diff image is generated locally for download.