CD-Extra

CD-Extra, also known as Blue Book as one of the multicolored "books" of optical disc standards, or CD Plus, is a standard for storing both audio and data on a CD.

An issue with storing images of such discs is that the ISO image is dependent on the specific sector layout of the disc (which depends on how it's partitioned into audio and data), and this structure is not stored in the file, leaving users of the imaged disc guessing as to how to intepret the image.

Links

 * Wikipedia article
 * Imaging CD-Extra / Blue Book discs