GD::SecurityImage versions through 1.75 for Perl use rand to generate secrets.
The random method creates the challenge text used for the CAPTCHA by sampling characters from an array using Perl's built-in rand function, and generates a (by default) six-character string.
The built-in rand function is unsuitable for security applications because it is predictable and reversible.
GD::SecurityImage has not been updated since 2018, the module is flagged as ADOPTME on CPAN, and the git repository is archived as read-only, which prevents issues and pull requests from being created.
Users are advised to find an alternative solution.
For users who are unable to migrate to an alternative, install Crypt::URandom::MonkeyPatch (which will override the built-in rand with a wrapper around Crypt::URandom) and apply the patch.