High dynamic range photography, combines several different photographs of the same scene into a single photograph.
The different photographs are taken at the optimum exposure settings for different parts of the scene.
Let's say you're photographing the Grand Canyon.
Because you'll be taking several photographs of the canyon, the camera, and the scene, must be stationary.
So, the camera is on a tripod.
You ascertain the clouds in the sky are imperceptibly moving.
You take a photograph of the sky using the optimum exposure for this part of the scene.
Next, you photograph the canyon wall, that's in the sun, using the optimum exposure for this part of the scene.
Finally, you photograph the canyon wall, that's in the shade, using the optimum exposure for this part of the scene.
Using software, you combine parts of the exposures.
If you shoot raw files, you can develop a raw file several times.
Each development optimizes the exposure for a different part of the scene.
Because you're working with a single file, movement in the scene doesn't present a problem.
You can use PhotoMerge Exposure to merge multiple exposures.
It's easy to go way too far with HDR.
Don't try to extract every once of dynamic range unless you truly want a surrealistic result.
The 10 Steps Every HDR Photographer Goes Through James Brandon
HDR Efex Pro Software
HDR PhotoStudio Software
High Dynamic Range (HDR) Landscape Photography Tutorial Royce Howland
LR/Enfuse Lightroom plugin
OpenEXR File format for HDR photographs