It seems like most of the other popular graphics frameworks/libraries have a facility for taking screenshots.
Do they? Sounds to me like quite a rare thing for people to want to do in their app! (And surely modern OSes have security restrictions that would stop apps from snapshotting other windows?)
But just to be clear, are you really trying to take an image of the OS desktop, or just your own app's window? Because if it's your own window then the Component class has methods to capture it to an Image.