In photoshop, you can take a picture and copy part of the image that has a cool texture, then create a brush from it. I'm using Painter IX. Can you do that in it and if so, how?
It's called dabs. You have to capture a DAB using the little triangle that pops up and gives you options. For the specific way to do it go into your painter help and just do a search on the word DAB and read the specifics. It's pretty easy but I found that painter tended to get glitchy as hell when it came to doing it. It basicly attaches the captured DAB to whatever brush your already using and then you have to go into the brush creator to edit up how the brush works. Good luck.