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image-deduplication-tool: simple tool to detect (and get rid of) similar images using perceptual hashing

There's gonna be a lot of duplicates in almost any arbitrary collection of images, and it can actually be surprising how many.

pHash lib, which is the core of the tool, easily detects cropped and retouched images, or same thing in different resolutions and formats.

Tool goes over the specified paths, calculating the hashes of all the images there, pickling them into a db file between runs (to save lots of time on re-calculating all of them). Then it just compares the hashes, showing closest results first.

pHash lib seem to be able to utilize multiple cpu cores for the hashing when built with with openmp flag, but it didn't seem to work for me, so put much simplier solution in place to scale such task - just forking worker pid for each hardware thread.

Optinally, tool can start handy feh viewer, where human can make a decision to remove one image version or the other (with pre-configured "rm" action) for each duplicate pair, skip to the next pair or stop the comparison.

Warning

As illustrated in #1 and CImg#49, libpHash/CImg will fall back to using potentially unsafe (exploitable with crafted pathnames) "sh -c" commands for non-image file formats and might not get filename-escaping correctly there (especially with CImg versions up to 1.5.3).

Simple safeguard for that particular issue would be only to run the tool on image paths (where CImg doesn't run "sh"), not paths that contain mixed-type files, or at least make sure there's no funky stuff in the filenames, script doesn't enforce any kind of policy there.

Note also that thing libpHash/CImg runs (usually) is ImageMagick's "convert", which can have all sort of issues with malicious file contents (see e.g. ImageTragick bug there), so maybe it's not a good idea to run the tool on a bunch of unsanitized images, ever.

One other precaution is that with the --feh option, script will run "feh" program, and --feh-args parameter may contain options (e.g. --info) that will be executed in the shell by feh, so either don't use --feh for weird and/or possibly-malicious (e.g. really weird) filenames or at least remove --info option from the --feh-args commandline.

Requirements

Usage

Just run as e.g. ./image_matcher.py --feh ~/media/images.

% ./image_matcher.py -h

usage: image_matcher.py [-h] [--hash-db PATH] [-d [PATH]] [-p THREADS]
                        [-n COUNT] [--feh] [--feh-args CMDLINE] [--debug]
                        paths [paths ...]

positional arguments:
  paths                 Paths to match images in (can be files or dirs).

optional arguments:
  -h, --help            show this help message and exit
  --hash-db PATH        Path to db to store hashes in (default:
                        ./image_matcher.db).
  -d [PATH], --reported-db [PATH]
                        Record already-displayed pairs in a specified file and
                        dont show these again. Can be specified without
                        parameter to use "reported.db" file in the current dir.
  -p THREADS, --parallel THREADS
                        How many hashing ops can be done in parallel (default:
                        try cpu_count() or 1).
  -n COUNT, --top-n COUNT
                        Limit output to N most similar results (default: print
                        all).
  --feh                 Run feh for each image match with removal actions
                        defined (see --feh-args).
  --feh-args CMDLINE    Feh commandline parameters (space-separated, unless
                        quoted with ") before two image paths (default: -GNFY
                        --info "echo '%f %wx%h (diff: {diff}, {diff_n} /
                        {diff_count})'" --action8 "rm %f" --action1 "kill -INT
                        {pid}", only used with --feh, python-format keywords
                        available: path1, path2, n, pid, diff, diff_n,
                        diff_count)
  --debug               Verbose operation mode.

feh can be customized to do any action or show any kind of info alongside images with --feh-args parameter. It's also possible to make it show images side-by-side in montage mode or in separate windows in multiwindow mode, see "man feh" for details.

Default feh command line:

feh -GNFY --info "echo '%f %wx%h (diff: {diff}, {diff_n} / {diff_count})'" --action8 "rm %f" --action1 "kill -INT {pid}" {path1} {path2}

makes it show fullscreen image, some basic info (along with difference between image hashes and how much images there are with the same level of difference) about it and action reference, pressing "8" there will remove currently displayed version, "1" will stop the comparison and quitting feh ("q") will go to the next pair.

Without --feh (non-interactive / non-gui mode), script outputs pairs of images and the integer Hamming distance value for their perceptual hash values (basically the degree of difference between the two).

Output is sorted by this "distance", so most similar images (with the lowest number) should come first (see --top-n parameter).

Optional --reported-db (or "-d") parameter allows efficient skipping of already-reported "similar" image pairs by recording these in a dbm file. Intended usage for this option is to skip repeating same hash-similar pairs on repeated runs, reporting similarity for new images instead.

Operation

Script does these steps, in order:

  • Try to load pre-calculated image hash values from --hash-db file.

  • Calculate missing perceptual hash values (ph_dct_imagehash) for each image found, possibly in multiple subprocesses.

  • Dump (pickle) produced hash values (back) to a --hash-db file.

  • Calculate the difference between hashes of each image pair for all two-image combinations, sorting the results.

  • Print (or run "feh" on) each found image-pair, in most-similar-first order, optionally skipping pairs matching those in --reported-db file.

It's fairly simple, with all the magic and awesomeness in calculation of that "perceptual hash" values, which is contained in libpHash.

Known Issues

pHash seem to be prone to hanging indefinitely on some non-image files without consuming much resources. Use ./image_matcher.py --debug -p 1 to see on which exact file it hangs on in such cases. Might add some check for file magic to see if it's image before running pHash over it in the future.

pHash also gives zero as a hash value for some images. No idea why it does that atm, but these "0" values obviously can't be meaningfully compared to anything, so tool skips them, issuing a log message (seen only with --debug).