You can make a PS brush out of just about anything ,but setting up your file correctly is key. It doesn't matter if you are using a photograph ,a render , or whatever you need to set up your Photoshop file in a way that will give you the best results for your brush.
Make a New File:
You may not need a BIG brush, but what if you need the same brush to be larger next time? It’s always a good idea to make your brush as large as possible in order to use it for other works later. If you use CS2 or CS3 you can make your file 2500 X 2500px. If you are running a previous version of Photoshop, you will be limited to 999px, or less. I have no idea of the size limits for any versions other then CS2 / CS3.

You can use a color image to make a brush, but it's easier to convert your image to Grayscale in order to get a better idea of what the brush will look like. When defining a brush preset Photoshop will automatically convert your selection to Grayscale to make the brush. White pixels will become transparent meaning you don’t have to erase the white pixels. Black pixels will be opaque, and everything else will be see-threw black/gray.
your image may need a little adjusting before it’s ready to be a brush. Here are a few adjustments you can make all found in the Image > Adjustments menu.
Levels

Brightness/Contrast

Curves

Shadows/Highlights

Exposure

Like I said before since Photoshop defines brushes based on a Grayscale there is no need to erase or clip anything. All you have to do is use the adjustments above ,and everything that is 100% white disappears. So put away your eraser/magic wand, and define your brush.
Make sure you have the correct layer selected and do a “select all” Command/Control + A. Go to Edit > define Brush Preset.

Then NAME your brush ,hit OK ,and your done. Your bush will be in you brush pallet as long as you don't reset it to default deleting all added brushes...
Have Fun ,and hope this helped.


