Professionally I think that Instagram is a great tool to help you promote yourself and your library. Take pictures of the library, patrons(with their permission of course), events and displays and let people know what is goin on at your library. I think that because Instagram started as a mobile app it is really keep the focus on its apps, the Android app is fast, easy to use, easy to connect to friends and share photos. More editing options beyond adding filters and captions would be nice, but it is a great tool to connect with your followers.
Another great app for sharing photos is Flickr. It has a similar idea as Instagram, but seems to be more powerful. It allows limited editing of your photos before and after you upload them. It also lets you connect with followers, see what other people are shooting, and most importantly what their camera details are. Flickr started out as an independent photo sharing website before being acquired by Yahoo! in 2005. It seems to be aimed at more professionals and enthusiasts rather then Instagram’s more casual user base.