[magick-users] Using identify for unique IDs

[duc.sequere.aut.de.via.decede at imagemagick.org]

> but it still takes a really long time

The signature is computed by iterating over every pixel in
the image.  ImageMagick Studio distributes the Wizard Toolkit
(http://wizards-toolkit.org/script/digest.php) which includes a digest
program that efficiently returns a signature as RDF:

  <?xml version="1.0"?>
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
           xmlns:digest="http://www.wizards-toolkit.org/digest/1.0/">
    <rdf:Description rdf:about="image.png">
      <digest:modify-date>2008-04-25T20:19:02-04:00</digest:modify-date>
      <digest:create-date>2008-04-25T20:19:02-04:00</digest:create-date>
      <digest:timestamp>2008-04-26T12:25:47-05:00</digest:timestamp>
      <digest:hash>SHA256</digest:hash>
      <digest:digest>78709afc0de69f51085675329dc44c8b475258c1e7fd29acea078347e641a020</digest:digest>
    </rdf:Description>
  </rdf:RDF>

However, as you suggested, it will return a different signature if the EXIF
data is changed.