How to Customize Your Photoshop Brush
You should first choose an image that you want to use as your brush and open the image in photoshop. The image should be relatively large.
Select the Rectangular tool and select (click and drag) the portion of the image you want to use as your brush.
Click edit, then find Define Brush Preset and click it (towards the bottom).
Name the image (something you’ll remember!) and click ‘OK’
Next, create a new file by clicking ‘File’, ‘New’, ‘OK’
On the toolbar on the left hand side, select the brush tool. It looks like a little paint brush.
There will be an options bar at the top of your screen. Click the little arrow next to the name of the brush you’re using. Scroll all the way down and select the brush that you just named.
Paint with your new customized paint brush!!! Enjoy!