It was revealed a few days ago that this following image could be a new wallpaper when iOS 11 is released likely in the fall.
Based on what the image looks like, which is basically a view underneath the ocean or a lake. With that said, it looks like a water theme. As for what that could entail for iOS 11, I have no idea, but it could mean that the next iPhone is more waterproof than the current iPhone 7 and 7 Plus.
This has not been confirmed to be the next iOS 11 wallpaper, but according to a source, it was leaked onto a tech blog (do not know specifically which one) but was removed. The fact that it is the size of a wallpaper that would work for both the 4.7-inch iPhone and 5.5 inch iPhone (Plus-sized) makes it look more credible.
To download the image on an iPhone or iPad, just put your finger where the image is, hold it there, and then wait for the “Save Image” button. If using a Mac, right click and save, drag to your desktop, or screenshot it (Command + Shift + 3) from the keyboard,