A new app called Snaphack allows you to save any and all photos and videos you receive through Snapchat without informing the person who sent it. The app is not affiliated with Snapchat and is currently available on the iTunes store for $0.99.
Here’s how Snaphack works: you download Snaphack app and log in with your Snapchat name and password. When someone sends you a photo or video via Snapchat, open it through Snaphack rather than through Snapchat and you’ll have it permanently in Snaphack.
Source: Huffington Post