This tool is most useful in combination with pnmcut. For instance, if you want to edit a small segment of a large image, and your image editor cannot edit the large image, you can cut out the segment you are interested in, edit it, and then paste it back in.
pnmcomp is, a more general tool, except that it lacks the "or," "and," and "xor" functions. pnmcomp allows you to specify an alpha mask in order to have only part of the inserted image get inserted. So the inserted pixels need not be a rectangle. You can also have the inserted image be translucent, so the resulting image is a mixture of the inserted image and the base image.
[ TIONS ]
The optional flag specifies the operation to use when doing the paste. The default is -replace. The other, logical operations are only allowed if both input images are bitmaps. These operations act as if white is TRUE and black is FALSE.
All flags can be abbreviated to their shortest unique prefix.