PhotoPresenter from Boinx Software is a new US$0.99 app that lets you display your photos from an iOS device to a big screen via a cable or using AirPlay to an AppleTV.
At first glance, this seems a silly expenditure, since you can use a cable or AirPlay to do that now, but PhotoPresenter has one very compelling feature in that you can display the photos in any order, rather than having to create a slideshow in advance. When you tap on any photo on your iPhone or iPad, it's displayed until you tap on another one. They can be in the order you choose. While your display device shows your photo full screen, you see all your photo libraries and can move between them while your last photo stays on display for your audience.
I can see this being very handy for on-the-fly presentations. If you are using AirPlay you want to be in the mirroring mode.
Even if you don't do presentations, the app is great for impromptu photo sharing. You probably won't want everything on your camera roll on the big screen, so you can pick and choose without anxiety.
I tried the app on both an iPad and my iPhone. The app ran fine under iOS 6 and iOS 7 beta. One thing to note: The instructions tell you how to invoke AirPlay on iOS 6, but iOS 7 does it differently using the new control center. If you don't know that, and if the instructions aren't updated, you may be stuck waiting for your photos to appear.
Other than that, PhotoPresenter is a very good idea at a very low price. I'm going to find a lot of uses for it, and you may too. Boinx has a lot of experience at dealing with photo apps such as FotoMagico 4 and TV production software like BoinxTV.
PhotoPresenter requires iOS 6 or later, is universal and is optimized for the iPhone 5.