Associating high res images with Open Graph objects

I'm building a testing app for the new FB Timeline and I've noticed that when an application posts activity to a user's timeline, and tha开发者_如何学Pythont user then 'features' the activity, the activity is displayed nice and widescreen but the image used is a scaled up version of the image defined in the og:image meta tag.

My question then: Does anyone know a way to associate a high res image with an open graph object so that it can be displayed nicely as a featured event on a user's timeline?