When building textures to use in modeling with Blender, some additional tools are handy outside of Blender. For instance, GIMP - GNU Image Manipulation Program can be used to process photographs to make them tileable, and also to create normal and deformation maps.
Some add-ons to GIMP to make this possible:
- Insane Bump: This is a normal map generator from a single image, originally created by omaremad. Load a single layer picture, then choose filters/map/insanebump..., tweak the details, then hit OK. The normal/height/ambiend/specular maps for the picture will be created within the folder where the original picture resides.
- GIMP normalmap plugin: This is a plugin for GIMP version 2.8.x. It allows you to convert images into RGB normal maps for use in per-pixel lighting applications. The goal is to completely clone NVIDIA's photoshop plugin, with a few new useful features.