We got a reject from Apple for this very reason.
Don't have an example but the dimensions for the photos below - best advised to avoid using these proportions! Physical = 3.5" x 4.25" 0.25 inch white border at the top, .1875 inches on the sides and .875 at the bottom
Google images keywords: polaroid frame, polaroid stack.
Sample: http://blog.simplyjean.com/wp-content/uploads/2007/11/polaro...
What's interesting that this wouldn't be allowed, I think there's many apps using this framing style in the app store already.