"The ImageMagick (IM) suite of command-line graphics tools is a
free software staple; Linux, other Unix-like operating systems, and
proprietary OSes like Windows have supported IM for close to two
decades. But there is also an alternative tool called
GraphicsMagick (GM) that covers much of the same functionality. How
do you know which one is right for you?
"Though IM traces its own history back to 1987, when it was an
internal tool developed at DuPont, the first public source code
release was in 1990. The core package is a collection of roughly a
dozen separate command-line tools: animate, compare, display,
identify, mogrify, and so on..."