The Clone tool allows you to paint one part of your image onto another. This
technique can be used to remove blemishes and foreign objects, such as airplanes
and power lines from an otherwise clear sky.
Clone Source
To start cloning an image, you must first define the clone source, which
is the point from which pixels will be copied. This is done by holding down the
Alt key and clicking where you want the clone source.
This can be repeated as many times as necessary.
Drawing
After selecting the clone source, you can simply paint with the clone tool as if
it were a brush. The thickness and shape can be adjusted for the desired level
of precision.