I think it would be good if the app was doing some pre-caching. As soon as the app starts it should trigger automatic ws calls in a thread. As it's javascript it's all asynchroneous, it should not be an issue.
An average student got no more than 20 courses, it would be piece of cake at the current stage of the app to execute most of the web service calls - and they are pretty much costing nothing in data compara to one image.

Overall it would make the app super fast.