HDR is High Dynamic Range photography. There are a number of real estate related sites that have mentioned HDR, some criticizing it as over-enhancement of images that mislead the viewer who will see something very different when they actually visit a home. While there are a great many things you can do with HDR software to enhance and even change a photo dramatically, I use it for the range of exposures that gives me better interior shots. You know the problems with lighting, and shooting toward bright windows. Those problems go away with HDR.
Basically, HDR is taking three or more shots across a spread of exposures, most commonly 1 stop on each side of the normal exposure. So, the center shot is normal, one shot is darker and the other lighter, as -1, 0, +1. The darker exposure shot will allow a better view through that bright window, with the interior going very dark. The brighter shot will bring out the darker areas of the interior, but the window will be blown out. It's the merging of the three with software that makes an HDR image and one that lets the photo show more like what the human eye sees. I like to take five shots each 3/4 stop apart, thus -1.5, -.75, 0, +.75, +1.5
There is an HDR group on Flickr, so I grabbed some shots that allow use with attribution. Clicking on them will take you to Flickr. Here is an example shot.
Without HDR, you'd either get a very bright window to see the interior curtains, or you'd get a normal look through the window, but the curtains would be totally dark. The merging of the images allows everything to be visible, though this image is still just a tad dark in my opinion.
In this next shot, the barn's interior is exposed very well, with areas back under the upper level showing good detail. And, the sunlit door at the rear still presents a view of what's beyond.
In this next shot, we get great detail around the window and the view through it as well. This one says it was done with in-camera HDR. I have a Pentax camera that I bought because it will take and merge the images in-camera. However, I found that I didn't like the result as much as doing it with software. There are a number of inexpensive HDR software solutions, and I settled on Dynamic Photo HDR for $55, number 2 on this review list. All I have to do is load the photos into the software, align them, then the software merges them to produce the finished image.
Many cameras will allow you to set up a multi-exposure process, where you just push the button and all three shots are taken without you having to change the exposure. You will need to use a tripod, as you must keep the camera very still. The photos get merged, and any movement will make that merge difficult or impossible.
As far as being misleading, you can do some really amazing things with HDR software, including making colors jump out, and grass greener, etc. While I do some fun things with my personal photos, I try to keep the real estate images as true to life as possible. It just makes the interior shots so much more lifelike, as the result is more like what the human eye sees, not the small exposure range of a single camera shot.
Here are a few more. I recommend HDR for real estate, and we all know how important those images are in our Internet marketing efforts.