Getting entity location on screen

I am making a mod to help people with PVP and I wondered if I could make it so that a red "dot" would show up on an overlay that corresponds to the location of the player. E.G. there is a player that is three blocks forward and one block to the left of you. I want a dot to appear on their head - only on your screen.

Is this possible and how would I do this?

Thanks in advance!

(Sorry for the post being a bit difficult to read (although being short)!)