Take your picture of the ball and load it up in photoshop. Get out the Zoom tool (Z) and zoom in. This isn't neccessary, but it helps. Get out the
Polygon Lasso tool
. If you can't find the Polygon Lasso tool in your toolbox, fear not. If you click and hold on this (
) tool, a menu will pop out where you can select the Polygon Lasso tool. Now, select around the ball with your Polygon Lasso tool. If you don't know how to select with the Polygon Lasso tool, check out
this thread. I explained the Polygon Lasso tool there. Anyway, once you have finished your ball selection, hit the copy button (or Ctrl+C).
Open up your other image that you want to apply the ball to and press the paste button (or Ctrl+V). It will automatically create a new layer with only the ball on it. The rest is transparent.
This may seem lengthly, but it isn't really.