Image capture software, like a lot of utility software, is of the sort in which 95% of the functionality you need is well-defined and shared by every program in the category. It comes down to those bells and whistles which most users rarely need--but you just might. HyperSnap does all of the basics, capturing windows, regions (rectangular or freehand), menus, and so on. It can scroll large images to capture an entire Web page, and of course you can save in a variety of formats. So what are the goodies?
HyperSnap's first standout extra feature is a text capture utility called TextSnap. Just select a screen region--for example, an error dialog with a complex string of hexadecimal numbers which mean nothing to you but might mean something to that guy in tech support--and use TextSnap. Presto, you've got the data in an editable text format. This is useful for a lot of things, but, unfortunately, it doesn't work in places where you might need it most--capturing text from PDFs or bitmap (JPG, GIF, etc) image files.
HyperSnap also has a "stamp" feature. This allows you to define an image and then "stamp" that image all over your captured picture. The stamp editor interface deserves some praise, as it does what I most desire in a user interface: It integrates choosing "which stamp" and "creating new stamps," so work flows naturally.
In comparison to Snagit, the generally accepted leader in screen capture, HyperSnap is close. Snagit has, overall, more options for image editing and capture. On the other hand, HyperSnap is ten dollars cheaper and performs the vast majority of functions you'll need just as well. If you don't yet have a preferred image capture program, it's worth checking out the trials for both.