I Was a Teenage Werewolf is a 1957 horror film starring Michael Landon as the titular creature, a James Dean-esque character who undergoes experiments by a mad scientist that turn him into a lycanthrope. The film's poster tells the viewer everything you need to know about the film, from the teenage character's rebellious ways - check out the greaser-esque dress - to his beautiful prey.
What makes this a cool poster is the Norman Rockwell-style artwork, though, accompanied by the gruesome bloody tears from the werewolf's claws. It's a great pairing that works well with the goofier film title, and apparently it helped put I Was a Teenage Werewolf into viewer's good graces: it was one of AIP's most successful films.
