The fractal images are often provided for granule (file) resources and they represent a unique visual representation of a file's checksum.

For example, a data file with SPASE identification spase://VHO/Granule/WIND/MFI/v4_PT03S/wi_h0_mfi_19941220_v04 has got a MD5 checksum hash value of AA33DB3256ED91BD2BF33B95E953CBF3 that was used to generate a fractal fingerprint image shown on the right.

On Linux, the image is created by invoking the following command:

echo 'AA33DB3256ED91BD2BF33B95E953CBF3' | visprint -b255 > image.png

where the visprint command reads the checksum hash value from STDIN and outputs the resulting PNG image to STDOUT. The above command redirects STDOUT to a file image.png.

The image will be different for almost every file with even slightly different contents because the checksums will differ significantly. Visprint uses the IFS fractal generation process, pioneered by Michael Barnsley. It is a way to create images which are self-similar to infinite depths. In other words, the picture is made up of smaller versions of itself.

The fingerprint images can be used to check differences in files but are not intended to substitute for the actual checksums. For serious security or integrity checking, a file checker tool should be employed instead.

Visprint project page provides download and more information about this fingerprinting tool.