Iska,
А! вот вы о чем! Не знаю какой тег. А команду нашел вот:
Binary Fields
The last type field that ID3Lib provides support for is a binary field. This holds miscellaneous data that can't be easily described any other way, such a JPEG image.
ID3_Field::Set()
отсюда:
http://id3lib.sourceforge.net/id3lib-manual.php
