Attributing photos is a huge part of designing online classes (since everything needs to be painfully copyright compliant). There is no easy way to add a caption to an image within Canvas without digging into the code which my Instructional Design team can't do. Cidi Labs already offers a way to easily add an alt tag - it'd be amazing if you also added a way to add a caption.
First off, congratulations on being the first poster to our new community forums! Send me your address and t-shirt size and I'll send you a Cidi Labs t-shirt (firstname.lastname@example.org). :)
Now on to your suggestion. It's a great one, and, in fact, one that we heard not long ago on a demo call. Shortly after that call Kenneth added the ability to add images with captions using our new HTML Snippets feature. Here's a video showing you this feature in action. Hopefully this meets your needs. If not, let us know how to improve it.
Awesome!! Thanks so much.