Open camera roll in exact photo

I am developing a camera application where I would like to add some features that are already present in the stock application. My problem is copying a small square in the lower left corner (in portrait mode), which displays a mini-sketch of the photograph that the user has just taken; then, when the user clicks on it, the photo application should open on the last photo stored in the camera roll.

I can upload a thumbnail of the latest photo in the camera roll using ALAssetsLibrary. I have access to it with [UIImage imageWithCGImage:[result thumbnail]]- but even if I have an ALAsset URL, I cannot open the photo application. I am trying to do this with:

[[UIApplication sharedApplication] openURL:result.defaultRepresentation.url];

But nothing happens.

I could display it inside my application with an additional UIView, but I think it will be easier and ... smarter to use the official photo app!

Can anyone help me? Thank you in advance!