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:
Ian Hubert’s famous video:
Free rock brushes:
https://bit.ly/3KpugR3
Tutorial:
https://youtu.be/w8dZl8uheKA