John Voorhees, writing for MacStories:

Unfortunately, the Instagram share extension’s functionality is limited. All you can do is add a title to the photo you post to Instagram. There is no way to crop your shot, apply filters, tag people, select a location, or select social networks on which to share your photo, all of which are available in the main app.

This really is a piss-poor implementation, if you ask me. Until they add more functionality, I’ll stick with my Push to Instagram workflow which allows for all of the features that Instagram’s own extension doesn’t.