Yes, technically snapchat pictures can be recovered on iphone. Here's how:
If you have a jailbroken handset then all you need to do is download and install something called "iFile".
It's a parogram that will allow you to ensure all snapchat images/videos stay in a folder called "temp folder" and saves them there as you go along. To be clear: This will not work on OLD Snapchat photos, but it's somethign you can do to save your photos as you go along from now on.
As I mentioned above though, this will only help you recover Snapchat photos if your handset is jailbroken. If it is not then:
There's another app called "Snapchack" which does the same thing for non jailbroken phones. Only difference is, it's like 69p on the app store, so not free!