There are some particular details that basically confirm most of the already available leaked iOS 8 photos. While the user interface of the interface looks different a photo that shows a different UI on a iPhone5S wouldn’t normally be enough to convince most people that it is a photo of iOS8. This is due to people being able to jailbreak their device and install a custom user interface.
The most recent leaked photo of iOS8 running on an iPhone 5s shows, besides the different interface, also some of the new iOS 8 applications: Tips, Healthbook, Watch Utility, a stand alone iTunes Radio application and TextEdit.
Also by now a lot of Apple engineers are most likely testing iOS 8 so that they have a chance to solve any left bugs before the WWDC 2014 when iOS 8 will finally be unveiled.