That design is from a manuscript that is 1200 years old. Current copyright is life of the author plus 70 years. Renditions of the art in various forms is public domain. My Daughter has that dove in her Book of Kells coloring book.

I agree it would be wrong to "make a copy of someone elses work and sell it as your own". The reason you see so many zoomorphic designs, that are original yet alike, at the games is that they are mostly taken from the old illuminated manuscripts.