Adding markers to Image with Pan & Zoom

[mkjorl]

Ive been working on a feature that allows you to place markers on an image along with the ability to zoom & pan the image.
I have all working as expected when the scale is "1", However once scale increases the marker is not placed in the correct location. Currently I adjust the translation based on the scale to get the point relative to the centre of the canvas when placing a new marker. The Y axis is correct however the X axis is not.
My assumption is that the aspect ratio of the canvas is affecting this. But I can't figure out how to apply the aspect ratio to get the correct position.

Code here (It doesn't seem to work unless run on your machine)