User blog comment:Vicyorus/HowTo:License files/@comment-11336324-20130717164806/@comment-4018164-20130717165255

Customs literally have copyright status as they are taken from graphic work that has been made by CP employees (with some exceptions like here, though customs are mostly more complex).

The "Custom work" license is just the Copyrighted Game license with another template that explains that this file is a "custom". It's easy if you want to look for customs of CP in the wiki.