Photos app is likely one of your most used apps on iPhone. There are no major user interface changes in iOS 9, but Apple has given the app some nice touches.
When browsing photo in the Camera Roll, you can now swipe down the photo to go back to the Camera Roll. This is much more convenient than having to tap the back arrow button on the left top corner.
When browsing photo in the Camera Roll, there is now a scrubber at the bottom. It is a minimized gallery which you can easily scroll through to get to the photo or video you want. Instead of swiping your photo one by one, you now can speed through the browsing using the scrubber.
Multiple photos selection is now easier on iOS 9. After tapping the “Select” in the Camera Roll, slide on the photo one by one to select them. This is much faster than tapping on each individual photo.
The Photos app now has deep Siri integration in iOS 9. You can use Siri to run searches based on dates, location or album names. For example “Show me photos from my trip to New York last winter”.
Finally this is a much sought feature. You can now pinch to zoom in to take a closer look in the video playing on Photos app.