O shit look at this mutha trucka postin artwork an shit like that. Dude, go on google and look up rock textures or pictures of fields of grass, convert it to greyscale or monochromatic , and lightly overlay those textures on the rocks and stuff. Just for shits and giggles, whats it going to hurt?
When I say overlay, I mean on a multiply layer, not an overlay layer. You probably figured that though. anyway! Unless you're on painter, then I've not a clue.