The harpies seem originally to have been wind spirits (personifications of the destructive nature of wind). Their name means "snatchers" or "swift robbers" and they steal food from their victims while they are eating and carry evildoers (especially those who have killed their family) to the Erinyes. When a person suddenly disappeared from the earth, it was said that he had been carried off by the harpies. Thus, they carried off the daughters of king Pandareus and gave them as servants to the Erinyes. In this form they were agents of punishment who abducted people and tortured them on their way to Tartarus. They were vicious, cruel and violent. The harpies were called "the hounds of mighty Zeus" thus "ministers of the Thunderer (Zeus)". Later writers listed the harpies among the guardians of the underworld among other monstrosities including the Centaurs, Scylla, Briareus, Lernaean Hydra, Chimera, Gorgons and Geryon. Their abode is either the islands called Strophades, a place at the entrance of Orcus, or a cave in Crete.
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.