MARBLEHEAD – One 13-year-old reader received a shocking and unwanted anatomy lesson this week, as she stumbled across a pornographic picture while thumbing through the pages of a popular novel intended for teenagers at the Abbot Library.According to library employees and television reports, the girl was reading a book from the “Gossip Girls” series when she came across a photo of adults involved in a sexually explicit activity, and it is not the first time it has happened at this library.”We have had a few incidents of someone placing explicit pictures in books that appear to be cut from magazines,” said Assistant Library Director Ann Connolly. “We are looking at this as a prank by someone who is not very mature, and possibly young.”Connolly said a parent brought the most recent photo to the attention of library employees immediately after it happened, and the library is now in the process of checking all of the books for more pictures.”We have spoken to that parent to make sure that she knows all of the books are being checked, and we do look out for this sort of thing,” said Connolly. “It is important for people to know that we are aware of this and we care very much that people feel comfortable when coming to our library.”Connolly said the library does watch out for this sort of prank, but it is not always an easy thing to police. She said employees have taken to some new methods of preventing this from happening again, but declined to comment on specifics to avoid copycat behavior.”We haven’t identified a specific person, but we are watching,” she said. “Hopefully this will not be occurring too many times.”Connolly said the library will be handling the issue internally, and did not contact police after any of the incidents. Employees are looking at the situation only as a childish prank, and not something more serious.