What software can I use to take screenshots with a set interval? I'd like to take screenshots every 2 second or so. Command-line and GUI are both ok.

I'd prefer software that can also resize and compress each screenshot.

EDIT:

What I realized I really wanted to do was take a screenshot and a picture with webcam at the same time. I ended up doing some python:

import threading
import os

def capture(i):
    i += 1
    threading.Timer(2.0, printit, [i]).start()
    fill = str(i).zfill(5)
    os.system("scrot scrot-%s.jpg" % fill)
    os.system("streamer -o streamer-%s.jpeg -s 320x240 -j 100" % fill)

capture(0)