A virtual graffiti wall that our customers can sign & doodle on

Firstly, please accept my apologies in advance if I’ve posted this in the incorrect place. I’m a total newbie to this community and I’m hoping to see if somebody could point me in the direction of how to do something to make this idea of mine a real thing!

Say if I wanted to add a virtual whiteboard that my customers can sign and doodle on. Anybody can add to the whiteboard and can’t edit / scribble over somebody else’s note or diddle. As more people add their piece to this virtual whiteboard I want it to expand so the amount of people who can add a piece to it would be unlimited.

Any ideas here where I might even begin researching this!

Thanks for your help