Picture shown at stat location

Hello everybody!
I am building my game's HUD and i find myself with a challenge.
I have an on-screen HP bar, the bar is upside down (as in, vertical) and i want an image to show at the top of it (current actor max HP) The thing is, his hp diminishes by second, so the image is supposed to descend as his hp does. (Because its supposed to be stuck at the current max hp stat) how to do that? I figure i have to work with x and y coordinates and maybe variables for current max hp but i am struggling :(