Today, Apple released iOS Version 4.1 for all newer iPhone/iPod devices. It introduces HDR for the built-in camera application. The make in HDR image, the application actually takes three pictures. One with the correction exposure, another one which is over exposed and the last one which is under exposed. The HDR image is then automatically generated from these three images.
The main advantage of HDR pictures, that a greater dynamic range of luminances can be represented. For example I took this picture of Entringen:
The normal mode picture is very dark in the lower region of the picture as the sky has some bright spots. The HDR mode picture doesn't show this problem. The problem of taking three pictures one after another is that non-static scenes can change between the pictures. As an example I took a picture of a flag waving in the wind:
The normal mode picture is fine, but the HDR mode picture shows the contours of the flag of the over and under exposed pictures.
As the iPhone saves the HDR and normal mode pictures at the same time, it is a nice to have feature.