Feature request: Fast paint

Hey,
I came up with this idea, tough, I don't know if anyone has requested it yet.

This would be a little button located near the emoji button. Perhabs with a keybind? It would open a window where you will get a blank surface to draw with. 10 different colors or so. 

When uploading and about to send a screenshot, this button would also come up. You would be able to press it and paint on the picture - example: You have a screenshot of gameplay and want to pinpoint a spot. You would then use the paint tool to fast and easily mark where he is. 

Theese modified pictures would be sent as normal pictures - Maybe they would be animated, so that you can add a reaction or something similar.