I'm developing an iOS app. I get collection of images from web, store them in Documents directory and want to be able to show them, say, as facebook app shows your photos. I think it uses native photos app of iOS. I've searched in apple docs and googled, but with no result. So, is it possible at all?
Facebook doesn't use the native photos app. It has built its own toolkit for that and have even open sourced their toolkit - Three20. It does have support for creating photo galleries for content based on the net so I imagine this will suit your use case. You can get started off by looking at tutorials already available on the net along with their documentation. Specifically look at this.