There are many tools to take/capture screenshots from command line in Windows.
If you are looking for command line tools in Linux – read this post.
Take screenshots of websites from command line in Linux
There are several ways to take screenshots in Linux. Most of them produce a WebKit, Gecko (Firefox) or khtml rendered screenshot image. Some of the methods require X session to open a window and take screenshots.
Read how to take screenshots from command line in Windows in this my post.