Many of the rich textures you see in the 3D realm are created in Photoshop using multiple images layered over each other. I use them a lot in my work. As an example the Victorian Era Street which is available in my store here at Renderosity uses a tiling wood texture that looks like it is old, weathered and has peeling paint on it. You can see the progression of the texture in the images in this tutorial but more importantly than the specific steps for making that one texture is the overall process of using overlays in your work.
Using the various blending modes Photoshop offers you can add a level of richness and authenticity to your texture. The appearance of rust, mold, cracks, a wood grain, and virtually anything you can think of can be made to look like it is part of the overall texture. Overlays are powerful and they should be used carefully or they can override the base texture. They are usually the last thing I incorporate into a texture.
While working with overlays may take the most time and tweaking, they are generally added later in the creation process, after a good foundation is laid. Using digital imagery will greatly enhance and speed up your work, but you don’t want it to be a crutch that you will always lean on, and they are not as flexible as created Photoshop layers. Using photo source should primarily be looked upon as the icing on the cake, not the whole meal. Building with a photo as a basis is building an inflexible resource.
To avoid some of the most common mistakes when overlaying images, keep these points in mind.