MD5 and SHA1 are common hashing function, which produce a binary or hex string. A visual hash works the same, but produces an image.
Like MD5 or SHA1:
VisHash GD is an implementation of a visual hash in php. It is free software, under the zlib/libpng OSI licence.
The vizhash of the string "hi" in different sizes:
| 16x16:|| 80x80:|| 128x128:|| 256x256:
| 32x32:|| Stretched vertically:|
| Stretched horizontally:
A few domain names hashed:
| facebook.com|| mozilla.com|| twitter.com|| commentcamarche.net
| google.fr|| siteduzero.com|| slashdot.org|| sourceforge.net
(Yes, I know it's ugly. But beauty is not the point.)
Vizhash_GD is under the zlib/libpng OSI licence.
Current version is 0.0.4 beta. It's only play-test code and could probably be improved, but it works.
An online service is available for you to test: http://sebsauvage.net/vizhash_gd.php - PLEASE DO NOT HAMMER THIS SERVICE or I will have to take it down. Do not hotlink images to this URL: Install the script on your own server. Thank you.
Many applications can be envisioned:
Edouard de Labareyre has developed a Java version of Vizhash GD which is visually compatible with the php version (This means that the generated images are the same between the Java and php version for the same input).