I believe that you have ever seen the HDR options on the top of your iPhone camera roll screen. It's a photo capturing mode that allows you to take photos with higher data rate. Sometimes when we travel around and find some scene wonderful, or sometimes when we want to take a beautiful selfie, you will find HDR mode useful. Let's see the pictures below to see what the difference is between enabling HDR or disable it.
I am sure that it is very obvious which one is captured with HDR enabled and which is not.
Now, let's see how to enable HDR on your iPhone:
Launch the Camera app on your iPhone and as you can see as the screenshot below, there's a HDR option on the top. Tap on it and the HDR option will turn orange.
Note: To take an iPhone HDR photos will take you for a while because in HDR mode the app will take several photos in different exposure time and pick out the best photos for you. Moreover, you can also turn on flashlight by taping on the first icon as the screenshot above shown to get a clearer iPhone photo especially at night.
That's it. Of course, there are other photo editing apps provided on iTunes Store or other app markets for you, you can fetch your favorite one to capture, edit or even share beautified iPhone photos with ease.