My programming sense is tingling and telling me that solving this problem is just patching a earlier poor decision. BUT I think it should be easy to solve anyway...
Given a resolution of X by Y, our screen looks like -
[0Y][XY] and needs to be converted to
to do this we need to take each set of coords X by Y and resolve them as (X, |Y-Y|).
No, translation needed.
//Getting screen Y size.
int maxY = gameContainer.getScreenHeight();
//Creating vector to describe image location
Vector2f imageLocation = new Vector2f(100, 250);
Image image = new Image("your/location.png");
//Draw to converted coords
If you are doing this for every Y... you probably want to create a convertY method to quickly change an array of images, etc to the translated Y coords.
But like I said- this is a bad idea.