Find duplicate photos and clean up
With this tool you can find duplicate photos without installing a program and without any image leaving your device: pick the photos and the tool groups identical files and similar shots (resized, re-saved, lightly edited). In each group the best image is kept and the others are marked as duplicates.
Source: Neal Krawetz – Kind of Like That (dHash, „difference hash“; Hacker Factor Blog). Updated: .
How it is calculated
The tool recognises duplicate photos in two ways: identical file content (SHA-256) and an image fingerprint that stays almost the same for resized or re-saved copies (dHash). Your browser calculates both itself; the photos are not uploaded.
How the comparison works
- Identical files: files of the same size are compared byte for byte via checksum.
- Similar images: every photo is shrunk to 9 × 8 grey levels and checked 64 times for “is the left pixel brighter than the right one?”. That yields a 64-bit fingerprint. The fewer bits differ, the more similar the images are.
- Strictness: “Similar” allows up to 6 differing bits, “very similar” up to 12 – that also finds burst shots and edits, but more false hits.
- Aspect ratio: cropped or rotated versions do not count as duplicates.
Which image is kept?
In each group the photo with the highest resolution is suggested, on a tie the larger file (less compressed). You can change every decision with a click. Then you download a list of duplicates (to delete in your folder) or a ZIP without the marked duplicates.
Limits
Web pages are not allowed to delete files on your device by themselves – that is why there is a list and a ZIP. Very similar but different pictures (two shots of the same scene) can end up in one group: check the preview before you delete anything. Comparing single-colour images is not meaningful and is skipped.
Frequently asked questions
How do I find duplicate photos on a PC?
Open the folder, select all photos (Ctrl + A) and drop them into the box or choose them via “Choose files”. The tool groups duplicates and similar images.
Are my photos uploaded?
No. The comparison runs entirely in your browser; there is no server. You can check it by disconnecting from the internet after the page has loaded.
How does the tool find similar, not just identical, images?
With an image fingerprint (dHash): each photo is shrunk to a tiny size and its brightness gradients are compared. Resized, re-compressed or lightly edited copies have almost the same fingerprint.
Can the tool delete the duplicates too?
No, web pages may not delete files on your device. You get a list of duplicates or a ZIP without the marked duplicates and delete or replace them in the folder yourself.
How do I find duplicate photos on an iPhone or Android phone?
The Photos app shows some duplicates itself (iOS: “Duplicates” album). With this tool you can also pick photos from your phone’s browser and compare them; for very large collections a PC is more comfortable.
Which photo should I keep?
Usually the one with the highest resolution and the largest file size – the tool marks it as “best quality”. Check the preview to make sure it really is the same subject.
Sources and legal basis
- Neal Krawetz – Kind of Like That (dHash, „difference hash“; Hacker Factor Blog)
- Wikipedia – Hamming distance
- MDN – SubtleCrypto.digest() (SHA-256)
- MDN – createImageBitmap()
- ITU-T T.81 / ISO/IEC 10918-1 – JPEG
As of: · Editorial policy
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