Yomichan for Chrome (think Rikaichan + auto flashcards)!

Rikaikun does this and its super useful but, looks like the plugin doesn't pick up alt attributes right now. It's useful to do that, since typically images have the alt set to any text in the image itself. 

The buttons here for instance: http://aoitori.kodansha.co.jp/book/2016/5/1.html