I think that "Image Slauth" is right place for this. Instagram photos and videos are now embeddable.  I don't like it despite the fact that embedded photos appear with Instagram username and clicking leads to page on Instagram.
http://www.creativebloq.com/design-tools/instagram-embeddable-7133533

Only photos that have been made public can be embedded. But, as we all know, there are ways around that.
http://help.instagram.com/116024195217477 Controlling Your Visibility on Instagram

I know but to me public images is very nature of Instagram. I can upload images to FB (friends only) if I want to keep them more or less private. I'm not frequent Instagram user but I'm annoyed by online world that changes to "free for use" fast.
Anyway watermark will help.