This is a quick tip on how to stop HDR from taking two pictures when enabled. Usually the iPhone will capture an HDR picture, and a non-HDR picture. This is done in case the HDR picture turns out to be blurry.
Nevertheless, most users end up having to delete the non-HDR picture every single time; which can get annoying and is a waste of time. This tutorial shows you how to stop saving the non-HDR picture too. It doesn't require a jailbroken iPhone.
Settings --> Photos & Camera
Then swipe down until you find the toggle 'Keep Normal Photo'. Toggle that to OFF.
Now to test if it worked, which it will, capture an HDR photo and check how many pictures were taken. Only one picture will be saved, which is the HDR picture.