Instagram recently made a change to their API policy which allowed developers to post pictures to the Instagram platform via their own app. Several other techniques we\'re p
Hipstamatic are one of the few apps that has been given write access via Instagram's API.
Instagram doesn't have a public API for posting photos, it lets you get their data but not write your own.
Hipstamatic and several other apps have negotiated special deals with Instagram that allow them to use the write API and post photos directly.
For all other developers you need to use iOS hooks to share to Instagram by switching to their app.
As far as I know its not easy to get Instagram to allow you write access- you would need to have a top app with high quality content and be friendly with the right people :)