A monster is a type of fictional creature found in horror, fantasy, science fiction, folklore, mythology and religion. Monsters are very often depicted as dangerous and aggressive with a strange, grotesque appearance that causes terror and fear. Monsters usually resemble bizarre, deformed, otherworldly and/or mutated animals or entirely unique creatures of varying sizes, but may also take a human form, such as mutants, ghosts and spirits, zombies or cannibals, among other things. They may or may not have supernatural powers, but are usually capable of killing or causing some form of destruction, threatening the social or moral order of the human world in the process. Animal monsters are outside the moral order, but sometimes have their origin in some human violation of the moral law (e.g. in the Greek myth, Minos does not sacrifice to Poseidon the white bull which the god sent him, so as punishment Poseidon makes Minos' wife, Pasiphaë, fall in love with the bull. She copulates with the beast, and gives birth to the man with a bull's head, the Minotaur). Human monsters are those who by birth were never fully human (Medusa and her Gorgon sisters) or who through some supernatural or unnatural act lost their humanity (werewolves, Frankenstein's monster), and so who can no longer, or who never could, follow the moral law of human society.
Chroma key compositing, or chroma keying, is a special effects / post-production technique for compositing (layering) two images or video streams together based on color hues (chroma range). The technique has been used heavily in many fields to remove a background from the subject of a photo or video – particularly the newscasting, motion picture and videogame industries. A color range in the foreground footage is made transparent, allowing separately filmed background footage or a static image to be inserted into the scene. The chroma keying technique is commonly used in video production and post-production. This technique is also referred to as color keying, colour-separation overlay (CSO; primarily by the BBC), or by various terms for specific color-related variants such as green screen, and blue screen – chroma keying can be done with backgrounds of any color that are uniform and distinct, but green and blue backgrounds are more commonly used because they differ most distinctly in hue from most human skin colors. No part of the subject being filmed or photographed may duplicate the color used as the backing.