What is “Chroma Key” for?
The Chroma Key option lets you remove the background of your camera by using a technique called chroma keying. Chroma keying allows you to take advantage of a chroma-compatible backdrop such as a green screen to immerse yourself within the game play footage.
You can access it by going to the Settings Tab and selecting Chroma Key as your Camera's background and adjusting sliders until you get your desired result:
Here is an example of what a camera feed looks like before applying chroma key:
And here is how it looks like after applying chroma key: