This website explains how subliminal messages work and we consequently understand how subliminal images are registered by our brain. In movies, pictures or video, flash images are inserted and we do not take conscious of this image but our brain detects on an unconscious point of view. Studies have been led such as the one of Vacary in cinema where he insert the words “eat popcorn” and the sales apparently increased. But this research was done under lab conditions and it does not prove clearly that subliminal images or messages can affect us.
Another study led in in 2009, at University College of London suggested that subliminal messages cant be received if the messages are negative. It is not really surprising because I have the impression that negative and hard images can easily be impressed in our mind. Chocking images are retained by our brain sometimes more than the good ones. For example trauma are easily registrered by people’s mind.