I am excited to have iPad access at Monroe elementary this year! One of the fun apps my kids and I have been playing with is Aviary (http://www.aviary.com/ios). Aviary is a free photo editing app with lots of fun tools like STICKERS! As is the case with most free apps, there are in-app purchases to give you even more options. Check out Cate's Aviary self portrait.
Self portraits with Aviary would be a fun class assignment! Students can create an alter-ego, or put themselves in disguise with stickers. They can also do more traditional photo editing with this app.