Caption Bubble allows you to pick any photo off the Internet (or one that you upload) and add a “bubble” to it and then add text. It can then be emailed, and the url can be posted on a teacher’s website, a blog or online journal.
There are a variety of web applications that provide this ability and more. I like this one, though, because it is very, very simple. That quality, along with the actually writing of appropriate text, makes it helpful to English Language Learners of all levels.