This poster is from the film 'Saw'
Most commonly known for its connotations with torture and pain, I think this poster fits in well.
The simple image creates a huge, cringing impact on the viewer. This makes them maybe feel some pain just looking at it (I definately can feel a toothache coming on...)
The image is a good representation of the film, as the same experiences are shared throughout all seven grousome editions. Any first time viewer with expectations from this poster would not have any disappointment.
Aside from the teeth, there is a very subtle reference to an actual saw at the top of the poster. This is to reiterate the name of the film, which has been made to look like part of the main image.
The same font for the film title is used in every film, so any returning Saw viewers would see this as an iconic image of the film.
The colour scheme is also very important to the poster. This is because every Saw film poster is essentially the same, with a different image to accompany it. Here are some examples