After looking I did come accross this post on the facebook forums:

link

They are feeding the facebook object a UIImage. That seems logical, but where is this documented? The API documentation is generalized to all platforms. Where are the iPhone specific requirements for arguments and their data types?

Thanks

**Update***** I still have not came across any API docs pertaining to Cocoa. I did, however, gather the information I needed by piecing together forum information, Facebook sample code, and some glue.

Hopefully they'll issue something a little more concrete over the next few months.