scrot

About scrot

From Debian's package description

scrot (SCReenshOT)is a simple command line screen capture utility. It uses imlib2 to grab and save images.

scrot has many useful features:

• Support for multiple image formats: JPG, PNG, GIF, and others.
• The screenshot's quality is configurable.
• It is possible to capture a specific window or a rectangular area on the screen.
• Other features.

Because scrot is a command line utility, it can easily be scripted and put to novel uses. For instance, scrot can be used to monitor a desktop PC in absence and register unwanted activities.

From Debian's description of the scrot package, under that package's license.