The process is called texture mapping. It is often done in coordination with UV mapping, which is performed in a 3-D modeling app. I have been working on this all year. I find that Blender 2.63 is my best choice for a modeling app. It is free, strongly supported by the community, and is upgraded often. It has a large learning curve, but there are many tutorials and lessons that can be found online. I use CGCookie.com to learn about Blender. They have many free tutorials, and also a paid subscription which allows you access to much more. It is well worth the $10 subscription fee. 

HTH

C~