What is the legality of selling collage prints?

I make collages using various images from different magazines and books and I’m wondering what is the legality of reproducing prints of the collages I make?

I want to be able to sell prints along with the original pieces but I want to make sure I won’t get in trouble before I get prints made.

I mainly use national geographic books and magazines but I also have a collection of other books that I’ve bought for collaging. What if I include a poem from a book? What is the legality on using writing from a book in my artwork?