This is the official movie poster for Paranormal Activity. It is quite a simple poster, yet captures the main idea of the film in the one picture. The film is about a couple who film in the bedroom whilst they sleep so they have evidence of any paranormal activity that happens whilst they are sleeping. So, in the image on the poster it shows the couple in the bed - where most of the film is filmed- and them looking at the open door as if someone is there who shouldn't be (however there isn't anyone that can be seen). The photo is also in night vision like from a hand held camera to show that most of the film is done at night and from a hand held camera.
The poster also features a quote so we get an idea of what a viewer thought of the film. The quote that is used is obviously going to be a quote that make the general public want to see it as this is the whole purpose of advertising from film companies.
There is also a sort of tagline on the movie poster saying "what happens when you sleep?" This question gives the public a good idea of what the whole story will be for the film if they don't really know anything about the film.
I also noticed at the bottom of the poster it has a thing saying about demanding the film to be shown at your local cinema. This is because the movie was originally shown at film festivals before its general release in the cinema. Where it wasn't a huge film, it wasn't shown everywhere but there was the choice to have it brought to your local cinema if enough interest was raised by the general public.