The answer is, it depends who you ask. According to Santa Fe attorney Saul Cohen, a national expert in copyright law and the arts, it's no problem at all. Collage is a recognized art form, Cohen said, which couldn't be created without appropriating the images of others.
Collage is a derivative work.
You can't use images without a license or permission. There's the myth that a creative work must be registered in order to be protected. The present law, which was adopted in 1976 and became effective in 1978, protects an original work for the life of its creator plus 50 years. Once the copyrighted period is over, the work reverts to the public domain and may be freely used. Anyone can paint Mt. Taylor, as long as they don't copy someone else's painting of Mt. Taylor.