The data of the attached picture.
 - If ID3AttachedPicture.mimeType is '-->' the data is an URL for a picture resource as a string. Otherwise the data is an ArrayBuffer.
The description of the attached picture.
The identifier of the frame.
The mime type of the attached picture.
The type of the attached picture.
 - See section 4.14 of id3v2.4.0-frames - ID3.org.
Represents an attached picture ID3 frame.