+1 more software should say what the copyright is.

On their github page, COPYING has a licence ( https://github.com/liuliu/ccv/blob/unstable/COPYING ). Looks BSDlike

It looks like they link to the GNU Scientific Library which is GPL so they need to have GPL compatible licence.

Yes, it is BSD 3-clause license. Added a link in front-page. As of GSL, I am not a guru on licensing, AFAIK, dynamic linking is a gray area and you can compile ccv without GSL dependency.