Notice that the file name appears just under the clone source buttons. This
is because you can actually select a clone source outside of the image that
you’re working on. Simply open a different file and set the clone source.
Then, when you go back to the primary file to paint with the Clone Stamp
or Healing Brush, the pixels from the other image will function as the
source of the clone.
Offset Options
The second section of commands in the Clone Source palette really
increase the variety of cloned results available to you. You can set exact
coordinates for the source, change the size of the cloned result relative to
the original source, tweak the rotation of the result and set a precise offset
(again, relative to the original source).
Tweaking the cloned results.