Yes, it's another technique. I can't find it right now (it's old masters technique). It's different from spritesheet or border radius, in a way that it requires image to be pre-proceed in photoshop via Filter->Offset, that basically acts as negative background position. This is to shift top-left pointer of an original image to its center. After that in CSS, you can use negative background-position to negate the image manipulation. Effectively it helps creating the right edge of a flexible element, which was difficult before background-position could be anchored to the right.

You'd still need multiple elements, but you'd have a single image (which is better for http latency/compression).