Best way to pull in posts from other sites on multi-install to populate front page WITH thumbnails?

Greetings,

I'm looking for the best way to have our multi-site WP's front page to be automatically populated with posts from around the network of other sites within the install...

The key difference here is I need to use thumbnails from those posts inside the template for the front page of the central site.

What's the best way to accomplish this?

Thanks,
Ray