It's cool that Apple's using your stuff, it's not cool they're not giving you attribution. I'd add a JGuitar url and copyright notice to all your images, so that this is displayed in Apple's results, and also call a lawyer.
I would also want to make sure Apple doesn't accidentally DDoS my service - I mean, if this gets broader use and if the service does not scale well this could be an issue. Or if it scales too well via AWS (doesn't seem the case here), there could be a huge surprise bill coming in.
If I'd use some non-public Apple API without asking them for written permission (or strip content from their site) I bet all hell would break loose.