What is HDR photography, and when might it be useful?
HDR (High Dynamic Range) can be called a technique where you take multiple shots at multiple exposures and combine them to get a perfectly exposed picture with best possible details. Its best applicable where the scene contrast is the most. For example, if you're taking a picture of the sky (bright) through the window of a dark room (dark), you have two options:
So, the workaround is, you turn on exposure bracketing (-2, 0, +2) of your camera, set the metering to evaluative and take 3 shots (continuous mode, self timer 2 second) of the scene from some steady place (tripod if possible).
Now if you use Photomatix or any similar software to merge these 3 shots into one, with minor adjustments you can get detailed sky as well as details window/room as well.
Here you can take a look at some amazing HDR photographs. http://www.stuckincustoms.com/hdr-photography/
Also, this is a great tutorial for the beginners: http://www.cambridgeincolour.com/tutorials/high-dynamic-range.htm
HDR is also known as High Dynamic Range. Usually it involves taking multiple pictures and combining them together, to increase the dynamic range of the camera. Specifically, a typical work flow is as follows:
For more information on making HDR images, see this question.