Segue is an amazing iPhone jailbreak tweak that allows you to add more animations to slideshow on Photos application on iPhone. The stock application allows the user to experience only a handful of animation effects when you use the slideshow feature in the Photos app.
Segue official description
From the makers of Photo Organizer 7 comes Segue, a novel tweak that adds customizable slideshow animations to the Photos app. Choose from 11 of Apple’s documented and undocumented transition effects, such as "cameraIris" and "pageCurl". Cycle through multiple effects, or have Segue choose random effects per transition. Best of all, it’s completely free and open-source.
Search for Segue on iPhone’s cydia store. This jailbreak tweak is free.