A monster is often a type of grotesque creature, whose appearance frightens and whose powers of destruction threaten the human world's social or moral order. A monster can also be like a human, but in folklore, they are commonly portrayed as the lowest class, as mutants, deformed, supernatural, and otherworldly. 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 the white bull which Poseidon sent him to the god, 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.