I've noticed it's not detected even if installed. This is due to api change. Adding
#ifdef CACA_API_VERSION_1
#include <caca0.h>
#endif
after
#include <caca.h>
in configure.ac and cscaca.h lets it compile but i don't really know how to test it

Migration info:
http://libcaca.zoy.org/manual/migrating.html