It is a form of GNU tar and generally you can use GNU tar to extract the image. Unless of coarse multiplexing was used. Then it's a whole new ballgame. Here is some interesting yet older reading on the subject:
Directions on how to use tar to restore data off of a tape. This example is based on the Solaris Platform.
http://seer.support.veritas.com/docs/205940.htm
Another document by Jason Consorti can be found here:
http://www.consorti.com/jason/netbackup_manual_tar_recovery.html
