I have a thing for old books, another thing for old woodcuts in old books, and yet another thing for old books with woodcuts of animals. Available on shirts, sweatshirts, cups, whatever at zazzle.
Click any image to see larger versions.
(All the original images are in the public domain.)
My process for working with old woodcuts is to clean up the image in Photoshop, removing things like paper texture and color, extra marks, and often the ghosts of type and images on the other side of the paper. In Photoshop I also work to get clear contrast and an image that has nothing but black and white (no grays). I then trace the image in Illustrator to get a vector image that I can refine by smoothing rough areas, repairing damaged parts, and redrawing missing or poorly done details. Illustrator is also where I play with the colors and, since vector images can be enlarged or reduced any amount without worrying about resolution, sizes of the images.
A few examples (click for full images and to fire up the animations if they are not animated):
