I need to get pictures of screens for reporting problems. I don't usually want to take the full screen or even a window - I want the smallest section that will show the problem. Using Ubuntu, I wasn't able to find anything that would do it as easily as I would like. I'm guessing with some certainty that I could have rigged The Gimp or something to capture the screen but then I would have to work at reducing the size, etc.
In How to choose the right screenshot program there was a reference to Ksnapshot. It installed with just one file, though it referenced khelpcenter as suggested. With a bit of clicking, I found that the "region" mode was what I wanted. It works nicely with Gnome-based Ubuntu.