Is it possible to programmatically upload a picture to twitter from iPhone?
Can this be done through twitter directly, or do I need to use a third-party service like Twitpic?
Thanks for editing your question. It makes more sense now. I'm leaving my original answer up so that this thread doesn't become confusing.
Anyway, the answer is short: the Twitter API doesn't provide a way for you to upload a photo directly with a status update, so I'm fairly certain you need to use a third-party service. The official Twitter client uses yFrog by default, but it lets you change the service to TwitPic, TweetPhoto, Mobypicture, Twitgoo, Posterous, img.ly, or a custom service.