Select a folder to scan. Supports images (JPG, PNG, GIF, WebP) and videos (MP4, WebM, MOV).
Everything you need to know about finding and cleaning up duplicate files with the aHash (Average Hash) algorithm. Scroll down for step‑by‑step instructions, tips, and answers to common questions.
Sakarto looks inside your images and videos to detect duplicates — not just files with the same name. The aHash algorithm converts each file into a compact 256‑bit “fingerprint” based on its overall brightness pattern. Files with matching fingerprints are grouped together, even if they were resized, re‑compressed, or saved in a different format.
Shrinks to 16×16 pixels and hashes in milliseconds. The best choice for very large folders where speed matters most.
Each file produces a 256‑bit binary fingerprint. Two files are compared by counting how many of those 256 bits differ — a single fast operation.
Image hashing runs in a background Web Worker via OffscreenCanvas — your tab stays fully responsive during scanning.
Reads the embedded EXIF thumbnail instead of the full image — 5–10× faster with near‑identical accuracy for most photos.
Average Hash (aHash) is one of the simplest and most reliable perceptual hashing algorithms. It reduces an image to its fundamental brightness structure in six steps:
Each image — regardless of its original size — is drawn onto a 16×16 pixel canvas. This makes all images directly comparable. In Fast Mode, JPEG files use their embedded EXIF thumbnail instead, which is faster and produces the same result in almost all cases.
Each of the 256 pixels is converted to a grayscale value using the standard luminance formula: 0.299×R + 0.587×G + 0.114×B. Color information is discarded. Only the brightness at each position matters.
The average brightness across all 256 pixels is calculated. Each pixel is then compared to that average: pixels brighter than average become 1, darker become 0. The result is a 256‑bit binary hash — a compact fingerprint of the image’s brightness structure.
To compare two files, their 256‑bit hashes are XOR’d bit by bit. The number of positions where the bits differ is the Hamming distance. A distance of 0 means identical hashes. The similarity threshold slider controls the maximum Hamming distance allowed for two files to be grouped together.
Before comparing hashes, Sakarto checks whether the two files have similar aspect ratios. Pairs where one file’s proportions differ by more than 10% are skipped entirely. This prevents a tall portrait from being matched with a wide landscape even if their brightness patterns coincidentally align.
For video files, 3 frames are extracted at 1.5‑second intervals. Each frame produces its own 256‑bit hash. The 3 hashes are averaged together (majority vote per bit) to produce a single representative hash for the whole file. Video scanning pauses if you switch browser tabs and resumes when you return.
The Similarity Threshold slider (0–50) controls how many bits two hashes can differ and still be grouped as duplicates. It is the most important control on this page.
Only nearly identical files match. Use for finding exact copies, the same file at different bitrates, or lossless vs. lossy exports. Very few false positives. May miss slightly re‑compressed or quality‑reduced copies.
Catches re‑saved copies, different resolutions of the same image, minor brightness adjustments, and JPEG compression artifacts. The default of 10 is a good starting point for most photo libraries. Some false positives are possible for images with very similar brightness structures.
Groups images with broadly similar brightness distributions. Two very different images can match if their brightness patterns coincide. Useful for finding visually related but not identical images. Expect more false positives — always review before deleting.
Click 📁 Select Folder to Scan to open a native folder picker (Chrome / Edge). Or drag and drop a folder onto the page. In Firefox or Safari, use the file input fallback.
A progress bar shows how many files have been processed. Duplicate groups appear live as they're found — you can start reviewing before the scan finishes. You can switch browser tabs freely during image scanning (videos pause when the tab is hidden and resume when you return).
After the scan, use the Similarity Threshold slider to tune how strict matching is. Releasing the slider re‑clusters all results instantly using the new value — no re‑scan needed. Start at the default of 10 and raise it only if you want to catch more approximate matches.
Results are shown in numbered groups. Each group contains files that look similar to each other.
Ctrl+Click two or more cards, then click ⚖️ Compare in the toolbar. A modal opens showing each file with full metadata, a similarity percentage, and action buttons. For 3+ files, a full pairwise similarity matrix is shown.
Select files and use the toolbar buttons. With Queue Mode on (recommended), files are staged for review first:
When Queue Mode is enabled (the default), clicking Move or Delete stages files in a queue instead of acting immediately. Switch to the Move Queue or Delete Queue tab in the sidebar to review what's staged, remove individual files, then execute when ready.
With Queue Mode disabled, a confirmation dialog appears and the operation runs immediately after you confirm.
| Button / Action | What it does |
|---|---|
| 🔄 New Search | Reload the page and start a fresh scan |
| 📋 Copy (N) | Copy selected filenames to clipboard. N = count selected. |
| 📂 Move (N) | Move selected files or stage them in the Move Queue |
| 🗑️ Delete (N) | Delete selected files or stage them in the Delete Queue |
| ✕ Deselect All | Remove selection from all cards |
| ⚖️ Compare (N) | Open the compare modal for Ctrl+clicked files. Needs 2+. |
| 🔇 Videos | Toggle mute/unmute for all video cards |
| Queue Mode checkbox | When checked: stage files for review before executing. Recommended. |
| Fast Mode checkbox | Use EXIF thumbnail for JPEG scanning — much faster. On by default. |
| Scan Images checkbox | Include or exclude image files from the scan |
| Scan Videos checkbox | Include or exclude video files from the scan |
| Similarity Threshold slider | Maximum Hamming distance for grouping. Lower = stricter. Re‑clusters instantly on release. |
| Click card | Select / deselect the file |
| Ctrl + Click card | Add / remove from compare list (purple border) |
| Click & drag (empty area) | Box‑select multiple cards at once |
| Ctrl + drag | Add to existing selection with box |
| Right‑click card | Context menu: Copy / Move / Delete / Compare |
| 🔍 hover icon | Open full‑size preview with metadata and action buttons |
| Hover video card | Auto‑play the video clip |
"aHash scanned my 18,000‑photo library in under 3 minutes. The threshold slider is genius — I started at 10 and found 1,200 duplicates. Nothing else comes close for speed."
"I manage a media archive with tens of thousands of files. aHash is my go‑to for the first pass — it's so fast that I can run it on entire drive roots. The Web Worker keeps the UI snappy."
"aHash found duplicates that other tools missed because it ignores colour and only compares brightness. I paired it with Color Signature for a two‑pass clean‑up — perfect combo."
"I was sceptical about aHash because it ignores colour, but it caught every duplicate in my holiday photos — different resolutions, crops, even some black‑and‑white versions. Fast and reliable."
Always back up your files before deleting anything. Deleted files bypass the recycle bin and cannot be recovered.
Fast Mode reads embedded EXIF thumbnails instead of full images — 5–10× faster with near‑identical accuracy for most photo collections.
Begin with the default threshold of 10. Review those results first. Only raise the slider if you want to catch more approximate matches.
In the Compare modal, check file size and resolution. A larger file usually means better quality. Keep the JPEG with the highest bitrate or the highest resolution PNG.
Use Move to a “Sakarto‑Duplicates” folder rather than deleting outright. Review the moved files over a few days before permanently removing them.
If expected duplicates aren't being grouped, try raising the threshold to 15–20. If results look too noisy at higher values, try a more precise algorithm like pHash or Color Signature.
Because hashing happens in grayscale, two images with the same brightness structure but completely different colors will match. This is uncommon in practice but can happen with high‑contrast graphics or images with bold geometric patterns. Always use Compare to verify before deleting.
A 90° rotation completely changes the position of bright and dark pixels in the 16×16 grid. Two versions of the same photo — one landscape, one rotated portrait — will produce very different hashes. Use ORB for rotation‑tolerant matching.
The File System Access API bypasses the OS recycle bin. Deleted files are gone permanently. Use Queue Mode to review before executing — it exists for exactly this reason.
Browsers throttle background video decoding. The scanner pauses video processing when the tab is hidden and resumes automatically when you return. Image scanning (in the Web Worker) is unaffected and continues in the background.
The File System Access API is only available in Chrome 86+ and Edge 86+. Firefox and Safari can scan and display results but cannot move or delete files. Use “Download List” to export results in those browsers.
Each hash is only 256 bits (32 bytes), so aHash uses far less memory than algorithms that store larger feature vectors. However, thumbnails rendered for display still consume RAM. For 50,000+ files, consider scanning subfolders individually.
remove() method, which permanently deletes files without sending them to the OS Recycle Bin or Trash. This is why Queue Mode is on by default: use it to stage files in the Delete Queue, preview each one using the full‑size preview icon, compare them side‑by‑side in the Compare modal, and only execute the deletion once you're certain. Move files to a “Sakarto‑Duplicates” subfolder first if you want a recoverable intermediate step.