Creating a "tiling" texture is a very useful skill for digital painters. This video introduces the basic concepts, and shows how a simple photographic tile can add gritty texture to a brush. This is a technique generally reserved for Texture Artists working in video games, but I've found it to be a versatile skill for illustration in general.

Reader Etheryte is kind enough to show alternative tiling texture technique in this video

AuthorMatt Kohr