Album Covers are provided for Audio Streaming Services such as SHOUTcast and Icecast. By default, the iTunes API will be used to obtain album covers when one is not provided. It is recommended, however not required, to include an album cover on all uploaded tracks rather than use the API.
The iTunes API is limited to 20 requests per minute however the MediaCP provides an intelligent caching mechanism that stores the album cover url locally for 24 hours and shares the cached URL across any service that plays a track with the same title/artist/album information. This mechanism drastically reduces the number of calls sent to the iTunes service and customers rarely reach the 20rpm limit imposed by iTunes.
An optional integration is also available for last.fm. You will need to create an account with last.fm and apply for a key to use this integration.