High Dynamic Range (HDR) photography is great for making the most from your iPhone's camera, especially in high-contrast situations.
With this feature, your iPhone takes multiple photos in rapid succession, each at a different exposure, and automatically blends them together. You get an image that has optimized highlights and really brings the shadows out of the noise, with way better detail in the bright and midtown areas.
When you enable HDR photography by tapping the HDR icon in the Camera app, your iPhone will save two copies of the image in your photo library: the “normal” image (without HDR) along with its HDR counterpart.
This can put a strain on your iPhone's storage, especially when taking a lot of HDR photos. If your iPhone's storage is low, or you're the type of person who likes to plan ahead, read this tutorial to learn how to turn off HDR photo duplicates and save significant amounts of storage space on your device.