While I normally use scrot attached to hotkeys using obkey for taking screenshots, for more complex screenshot tasks Imagemagick's import is an indispensable tool. For some reason, the man page for import on my Arch Linux system doesn't show the complete listing of all available options. A full listing requires one to refer to several different resources (here and here).
Say, for example, that we want to take 10 full-screen screenshots every second starting in 10 seconds and save the files in the ~/Images subfolder with the name snap.png. With imagemagick import we can do this with the following command:
import -window root -delay 10 -snaps 10 -pause 1 ~/Images/snap.png
-window root tells import to take a screenshot of the entire screen
-delay 10 tells import to wait 10 seconds before starting to take screenshots
-snaps 10 tells import to take 10 screenshots
-pause 1 tells import to wait 1 second between snaps
import will automatically number the screenshots snap-0.png ~ snap-9.png