pamcomp(1) on Linux
The text 68339d1a0599, as Debian 13 (Trixie), Debian 12 (Bookworm) shipped it.
composite (overlay) two Netpbm images together
Flags it lists
-
-align -
-alpha -
-invert -
-linear -
-mixtransparency -
-opacity -
-valign -
-xoff -
-yoff