I agree, the stamps are attractive looking, but even still, there are a few concerns that I guess the USPS and those involved in the printing of the stamps overcame:
1. It's curious that the Postal Bulletin suggests that the colors used for the stamp are black, cyan, magenta and yellow. I guess a combination thereof makes for the orange color that is shown on the major portion of the stamps.
2. I also find it curious that the only disclaimer shown on the pane of stamps is that "Name, image and likeness of Janis Joplin used under license." It would seem that it wasn't necessary to credit the photographer (David Gahr) for the photograph(s), especially the large one shown on the reverse of the stamp issue:

3. Even though tagging, etc., is supposed to avoid problems such as this, concern has been raised on other sites wondering if postal clerks will recognize these as legitimate stamps or think of them as "labels" and not legitimate postage. The words "Forever" and "USA" written in psychadelic print don't help either.
Nonetheless, the bottom line is that I'm sure the stamp issue will sell well and that's what the USPS is concerned about.