Licence Exemption
Although ssdeep and the fuzzy hashing API are usually licensed under GNU GPLv2 Jesse Kornblum has licenced them to PECL under the terms of the Perl Artistic Licence with the following declaration:
I hereby license ssdeep, the current version and all subsequent versions, under the terms of the Perl Artistic License, for inclusion into the PECL.
Jesse Kornblum - verbatim email