Facebook just announced a new Open Graph "Like" action that will make it easy for developers to build Like buttons into their apps. Interestingly, you can make the button look however you want, or hook it in to a "thumbs up" or heart icon you've already implemented in your app — like in Instagram or Foursquare's case. Likes inside mobile apps will now show up in your News Ticker, News Feed, and notifications drop-down menu as if someone liked a picture or status you posted right there on Facebook. Previously, when you liked someone's post inside an app like Instagram, the like would stay inside that app.
The update comes as part of a long line of Open Graph integrations like Action Links ("Save This Place" in Foursquare stories) and integrated location data APIs that drive traffic back to Facebook from mobile and web apps. These actions create a full circle of interaction between Facebook and apps, but as of today, Facebook is no longer approving custom "Like" actions inside apps — developers must now use Facebook's official Like action, though they can make the button itself look however they'd like.