Free Online Image Similarity Checker — Compare Two Images
Compare two images and get an accurate similarity score with our free online image similarity checker. Upload any two images, and our tool analyzes them pixel-by-pixel to calculate a percentage similarity score, Mean Squared Error (MSE), and Peak Signal-to-Noise Ratio (PSNR). A visual diff overlay highlights exactly which pixels differ. Perfect for designers verifying image exports, developers testing image processing pipelines, photographers comparing edited versions, or anyone who needs to quantify how alike two images are. All processing happens locally in your browser.
Upload the first image and the second image you want to compare.
View the similarity score, detailed metrics, and visual diff overlay.
Use the swap button to reverse the comparison, or upload new images to compare again.
Tips for Comparing Image Similarity
- For the most accurate results, use images of the same dimensions. Different sized images are normalized to the smaller canvas.
- A similarity score above 95% means the images are nearly identical. Below 80% indicates visible differences.
- The difference overlay uses a color highlight to show changed pixels — great for spotting subtle edits or compression artifacts.
Frequently Asked Questions — Image Similarity Checker
Is the image similarity checker free?
Yes, completely free. No registration, no hidden charges, and no watermarks. All processing happens locally in your browser — your images never leave your device.
How is the similarity score calculated?
The tool compares images pixel-by-pixel by subtracting color values at each position. The similarity score is the percentage of pixels that fall within a small tolerance threshold. A higher score means more pixels match.
What do MSE and PSNR mean?
Mean Squared Error (MSE) measures the average squared difference between pixel values — lower is better. Peak Signal-to-Noise Ratio (PSNR) expresses the ratio between the maximum possible signal and the MSE in decibels — higher (above 30 dB) indicates better quality preservation.
What image formats are supported?
The tool supports all common image formats including JPG, PNG, WebP, GIF, BMP, AVIF, SVG, and more.
What if my images are different sizes?
The tool automatically normalizes differently sized images by centering each on a shared canvas filled with white pixels. For the most accurate pixel-level comparison, we recommend using images of identical dimensions.
Can I download the comparison result?
The difference overlay preview is shown directly in your browser. You can right-click and save it, or take a screenshot for your records. The tool focuses on real-time analysis rather than file storage.
What does a 'good' PSNR score look like?
For image comparison: 40+ dB means the images are nearly indistinguishable (excellent), 30-40 dB indicates good quality with minor differences, 20-30 dB shows noticeable differences, and below 20 dB means the images are significantly different.