Try to do this: (I didn't test yet)
- ATImageBox has the public prop Image: TImage
- in the MouseMove event, get X/Y params, and do conversion from screen coords, to Image related coords. Like
P:= ATImageBox1.ClientToScreen(Point(X, Y));
P:= ATImageBox1.Image.ScreenToClient(P);
now you have P. Image related coords. Read the zooming value (prop ImageZoom, in percents) and scale P.