
I ran across this photoshop tutorial last semester and I use this method to create brushes for textures and photoshop work. Thought I would post it up for anyone that might find these useful. Most the brushes used in my concept art are from different stock photo's that I took around grand rapids with my Sony point and shoot before it died.
This is a great way to make grunge or dirty brushes and some you find to have a ton of uses.
I actually have a photoshop action setup that I run on an image I am planning to use as a brush and then modify the image for whatever purpose. The action performs all the invert/levels/saturation changes in one click. Erasing away parts of a new brush with an already good brush can also make way for tons of variations of your brushes. Usually this is how I will end up with more interesting and useful brushes.
The pic above is of one of my better brushes, and this is typically one that I will use later to create others. The picture is from a warehouse by my apartment.
Here is the tutorial that will tell you how to make 2500x2500 brushes
http://www.bittbox.com/photoshop/how-to-make-a-photoshop-brush
Also another that shows the technique of using an earlier created brush to enhance another. In case that doesn't make sense how I explained.
http://www.myinkblog.com/2009/06/10/how-to-create-your-own-photoshop-brushes/
I'm also reading through 3dTotal.com's Digital Paining Techniques book that describes these type of brushes more in depth as well as technique of course. If anyone wants to take a look at it I'll bring it to class, I would lend it out but I'm working on textures now and will use it.