A quick and dirty alternative to photoscanning.
While this method might not work for everything, it very often does the trick and takes only minutes (depending on the complexity of the mesh).
Watch how I got the textures and also download them for free:
• Create a Castle Ruin in Blender and U...
Ian Hubert's famous video:
• Modeling Buildings in Blender- Lazy T...
Free rock brushes:
https://www.blendswap.com/blend/20195
Tutorial:
• How to Easily Make Rocky Surfaces in ...