To clarify, do you wish to develop an app where the users can specify virtual backgrounds to be used in meetings (ahead of time), or are you looking to develop an app that works in-meeting, near real time?
The latter is not yet possible, but is coming soon!
In this case, this should be possible by creating an OAuth App:
This would allow you to request access to view/manage a user or account’s virtual backgrounds via API. You’d receive an access_token from authorized users which would allow you to then call our Virtual Backgrounds APIs on their behalf, as part of your app:
Let me know if this helps to point you in the right direction!