#greenscreen 

noun (in film and video techniques such as chromakey) a green background in front of which moving subjects are filmed and which allows a separately filmed background to be added to the final image. "scenes with green screen effects"  

Chroma key DescriptionChroma key compositing, or chroma keying, is a visual effects/post-production technique for compositing two images or video streams together based on colour hues. Wikipedia  #Howdoesgreenscreenwork ? All of this high-tech fakery happens with the help of backdrops of brightly colored fabric or paint, and a process called "chroma key," also referred to as "green screen" due to the backdrops' color, which is typically a vivid green. ... #Chromakeying isn't just for backgrounds; it works with objects, too.Aug 18, 2016  green screen films include  The Great Gatsby. The Avengers. The Hobbit. Alice in Wonderland.