Here are some images I used as visual reference:
After observing the trends within these images I decided to try to roughly sketch out how it could be applied to the day of the invisible cannibals from beyond the stars. I would rather the poster be more simplistic than overdone, a few basic stand out images with a single tone background.
This first sketch was just an idea which I dont think works for the film, but is interesting so I thought id post it anyway. It shows one of the Cannibals faces (of which we dont see in the film) with scars and blood, however his face also is held within an image of the Earth, which represents the threat the cannibals have of invading it. This "world" would also be placed as the visor of a spacemans helmet, so it would be somewhat of a three peice structure behind one image.
After this I decided to follow the more traditional poster look, with a simple design yet retro feel. I decided on a few key aspects of the film which could be used effectively as an image on a poster. This first one is a spacemans helmet, sitting in a pool of blood. I thought this described the moment when the cannibals take off their spacesuits to become fully invisible and start attacking innocent humans.
This poster is based on the structure of the poster above, however with a different key aspect of the film which gives impact of what to expect. You can see the crashed spacepod, with an astronaught walking out of it and a man running away in fright. I have also started using a line stating the film is coming soon, any suggestions on what could be used are welcome as my lines pretty cheesy.
This next image is far more typical to the 1950's horror movie poster - the subject of the female being weak and in need of some kind of heroic assistance, indulging in the subject of how gender equality has changed over the years.
Last up is the most daring and probably unfavourable image that came to mind, which is based on the visual refrence of the film "Aliens" and uses understanding of how they worked with their inhumane ways of eating their prey.