The new contrib fixes a bunch of reported CVE:

    CVE-2021-30498  (tga export, not concerned)
    CVE-2021-30499  (troff export, not concerned)
    CVE-2021-3410   (canvas.c, v0.99.beta19)
    CVE-2018-20546  (dither.c, v0.99.beta19)
    CVE-2018-20547  (dither.c, v0.99.beta19)
    CVE-2018-20545  (load_image, v0.99.beta19)
    CVE-2018-20548  (load_image, v0.99.beta19)
    CVE-2018-20549  (caca_file_read, 0.99.beta19, not concerned)

See release note[^1] on the github project.

It also allow to migrate the use of the new API instead of libcucul,
which has been merged into libcaca since 0.99.beta15:

    commit f61816ceb7445f8bf818936151554ac060764b39
    Author: Sam Hocevar <sam@hocevar.net>
    Date:   Sat Sep 27 13:12:46 2008 +0000

    Starting refactoring to get rid of libcucul. The initial reason for the
    split is rendered moot by the plugin system: when enabled, binaries do
    not link directly with libX11 or libGL. I hope this is a step towards
    more consisteny and clarity.

It was then completely wiped out by the following commit, which is part
of v0.99.beta20:

    commit 5f0ec215f8c9915ed028324a8ecac8212f68e18d
    Author: Sam Hocevar <sam@hocevar.net>
    Date:   Thu May 3 10:33:30 2018 +0200

    Remove legacy code from 10 years ago.

Check NEWS for details:

    \section news0_99_beta15 Changes between 0.99.beta15 and 0.99.beta14

     - libcucul was merged back into libcaca for more clarity

[^1]: https://github.com/cacalabs/libcaca/releases/tag/v0.99.beta20