Screen Grabber is a small, simple and free program that requires no installation, and which lets you automatically take a series of consecutive screenshots.
It works minimized to the Windows taskbar, from where you can activate it to start taking the shots. In Screen Grabber you can configure it to save, in the file of each shot, the time and date each one was taken.
Screen Grabber lets you save the shots in various graphic formats, and with different quality levels.