For a derivative work to be copyrightable, it must be "different enough" from the original works that it can be considered a new work in its own right. For most collage artists, this is not a problem. The very nature of collage generally involves combining multiple elements to create a new whole.
http://www.funnystrange.com/copyright/derivative.htm

"To go to my grave without knowing whether it was lack of talent or lack of perseverance that failed me, without feeling that I'd probed deeply, without sucking the joy out of hearty work, that would be self-inflicted pain I could never forgive myself for." - Susan Vreeland, "The Forest Lover"(p. 275)

"I don't make poetry by the day or week, but by the years." - Robert Frost

Compromise : The art of dividing a cake in such a way that everybody
believes he got the biggest piece.
Classic : A book which people praise, but do not read.
Philosopher : A fool who torments himself during life, to be spoken of when dead.
Opportunist : A person who starts taking bath if he accidentally falls into a river.
Optimist : A person who while falling from Eiffel tower says in midway "See, I am not injured yet."