Should be a default option in the native script. Works great, doing exactly as described. It allows your shares to use the actual image in the thread instead of the default logo. Makes for a much more interesting share on your timeline or your FB page.
This is very helpful and is exactly what I was needing since sharing to FB and Twitter are a big deal. One issue I'm having with it is I notice that while I can see the image when I click on the tweet directly, it doesn't seem to show up in a timeline.