How chromakey works is quite easy to understand, Basically you put the subject in front of a usually solid green background, and the system substitutes green(the key colour) for the desired background image or video. A drawback is, the subject can't be wearing any green coloured clothing, because that would change to the background image, and would sort of become invisible. This is very much a real time process.
There are chromakey apps already available for Android, and most video editing programs on computers can do chromakey as well.
