I've recently discovered DropCopy, from 10base-t Interactive. This little utility's "window" is a small translucent dark spot, rather like a hole, that sits behind all other applications (and behind your desktop Finder icons)

Part of writing about the Mac involves taking screenshots - lots and lots of screenshots. Anyone can snap a screenshot by pressing Command-3 to capture the entire screen or Command-4 to specify an area to be captured, but when you're creating hundreds of images, those tools are too blunt