Oh. I got Yosemite and CC, so let's explain how to do this.
If you are finished with the Brush Tool and you do not want to accidentally paint another picture, just click on the Hand Tool, and the Paint Tool will be deselected. You can also use the keyboard shortcut "h". When you click and drag on an over-sized image, the Hand Tool just moves it around.
When you want your Brush back, just click on it again.