Since you can store literally thousands of photographs on your iPhone, you might find it most convenient to view them in a slideshow, where each picture appears on the screen for a few seconds before automatically switching to a new picture. By viewing pictures as a slideshow, you won't have to switch pictures manually.
When defining your slideshow, you can modify four options:
How long each slide appears on the screen
The transition time between each slide
Whether or not to repeat the entire slideshow
Whether to display pictures in order or at random
To customize a slideshow, do this:
From the Home screen, tap Settings. The Settings screen appears.
Scroll down and tap Photos near the bottom of the ...