WebShot is a freeware software for Windows that allows you to take screenshots and thumbnails of web pages or whole websites in the following image formats: JPG, GIF, PNG, BMP.
It also features a command line interface (webshotcmd.exe) for taking batch screenshots/thumbnails.

Some of the switches are:

/url Website url
/in Text file with urls on each line
/out Output image file
/width Image width
/height Image height
/quality Quality of output image (0-100)
/encoder Image encoder (ie. png, gif, jpg, bmp)
-verbose Displays detailed browser information

And more……..