Free Online Image Compare Tool

Online Image Compare Tool: Pixel Diff, Highlight Map, and Slider Comparison

This image compare tool helps you find visual differences between two images. It is useful for design review, screenshot regression testing, UI change checks, marketing image revisions, product photo edits, and before-after comparisons. Upload two JPG, PNG, WebP, or BMP images, and the tool compares pixels locally in your browser, generates a highlighted diff image, and reports changed pixels, difference percentage, canvas size, and whether the original dimensions match.

What This Image Compare Tool Can Detect

The comparison is pixel based. If the color, transparency, or content at the same position is different, the pixel is counted as a change. This can reveal:

  • Button, text, icon, spacing, shadow, or background changes in screenshots
  • Misalignment, missing areas, cropping, or scaling problems in design exports
  • Color and detail changes after compression or format conversion
  • Local edits between original and retouched product images
  • Visual regression issues in automated screenshot testing

The default view is a highlighted diff map. You can also switch to slider comparison and drag between the two aligned images for manual review.

How to Compare Two Images

  1. Upload the left image, usually the baseline, old version, design file, or original screenshot.
  2. Upload the right image, usually the new version, actual screenshot, edited image, or compressed image.
  3. Adjust the difference threshold. A lower threshold is more sensitive; a higher threshold ignores more minor color changes.
  4. Enable anti-aliasing ignore for screenshots with text or thin edges to reduce noisy edge differences.
  5. If the images have different dimensions, choose center alignment, top-left alignment, or stretch-to-first-image alignment.
  6. Run the comparison and review the highlighted diff, slider comparison, and statistics.
  7. Download the highlighted diff PNG when you need a shareable visual report.

Choosing an Alignment Mode

If both images have the same dimensions, center and top-left alignment usually produce the same result. If dimensions differ, alignment matters:

  • Center alignment works well for designs, posters, and images with centered content.
  • Top-left alignment works well for web pages, app screenshots, and UI layouts that start from the top-left corner.
  • Stretch to first image works when the visual content is similar but exported at different dimensions.

For screenshot regression testing, keep the same browser, device pixel ratio, viewport size, fonts, and rendering environment whenever possible.

Threshold and Anti-Aliasing

This tool compares pixel values, not semantic meaning. Browser rendering, fonts, shadows, rounded corners, and JPG compression can create small differences. Threshold controls sensitivity:

  • 0.00 to 0.05: strict comparison for PNG screenshots and precise visual regression.
  • 0.06 to 0.15: good for most UI screenshots and design checks.
  • 0.16 or higher: better for JPG images, compressed images, and cases with acceptable color drift.

Ignoring anti-aliasing can reduce false positives around text edges and diagonal lines, but the tool still performs pixel-level comparison and does not understand whether two visuals are functionally equivalent.

Privacy and Performance

Image loading, pixel comparison, and diff generation all happen locally in your browser. The images are not uploaded to a server. Very large images may use more memory because the browser needs to hold both images and the diff image as pixel buffers. For extremely large files, resize or compress images before comparing them.

Useful Search Terms

Image compare, image diff, pixel diff, screenshot compare, visual regression testing, design comparison, compare two images online, highlight image differences.