Intelli Hash is a powerful app to get hashtag suggestions from images. It uses powerful image recognition API from Imagga. The app is open source.
Using the Intelli Hash app, you can not only get suggestions for hashtags but also copy and share these hashtags on other media.
Sorry iPhoners… only Android at the moment 🙁 https://play.google.com/store/apps/details?id=hashtags.autohash