Copyright Infringement concerning pictures and movie stills?

Ok....so I want some movie posters, but I cannot find any that I like the pictures of and are in the right size. Is there a copyright infringement problem with printing the pictures out at Walgreens or something and putting them up in my room? Is that illegal or bad? Is it still illegal if you print them from your home printer? I know absolutely nothing about this....does it depend on the picture?