Contact your printer to get their list of size and resolution requirements. I just altered a photo for my first image to be used on a billboard, and come to find out it only needed to be 9ppi!! Yep, if you scan a 4x6 as a 4x6 at 300ppi, you can make an 11'x16' billboard! And when you ask them what size they need, if they tell you "it should be 300ppi" (drives me nuts when they do this, and you'd be amazed at how often they do this!) make sure they understand that is the 3rd part of a 3 part equation. Respond with, "How many inches by how many inches, at 300ppi?" Good luck and happy Photoshopping- -Lew ;-)