Right off the bat, you'll notice that the layout is not the usual 4 icons across that has been the standard for iPhones since the first one was released back in 2007. The layout is a 5 x 7 grid, and even more interesting is that the resolution of the image is 1,600 x 966, which is not a resolution that you'd find in the iOS ecosystem, or really anywhere else for that matter. A resolution like that would mean a PPI of close to 400 on a 4.7-inch screen, and it is around a 16:10 aspect ratio. That's not quite the 16:9 widescreen movie ratio that Apple has been using for the past couple iPhones, but it is closer to it than to the 4:3 ratio seen on the iPhone 4s and older.
Healthbook app, CarPlay, and even something labeled as "Watch Utility", which would seem to be hinting at the oft-rumored iWatch. It should be noted that there's no sign of the Preview, TextEdit, or Tips apps that were seen in another recent image that claimed to show iOS 8.Beyond those clues, there are also a few apps on the home screen that haven't been part of the pre-installed collection before like the iWork suite (Pages, Numbers, Keynote), the iLife apps (Garage Band, iPhoto, iMovie), the rumored
It's hard to say how much we believe that this screenshot is real. A lot of it looks good, but could have been put together based on rumors. The error level analysis doesn't appear to show any blatant photo editing though. The one part that looks way off-base is the "Watch Utility" app, which has an icon that Apple would never release, but since the app is likely still in early development, that's not too surprising.