I can get rid of this by making the ctrlDiv offset as hidden, but then this removes the bottom scroll bar completely in all browsers (not really useful if the document is bigger than the browser window).
I have read about putting the image as a background image of another element, but cannot for the life of me get this to work at all.
Also, the functions to return the absolute position of elements (and mouse pointer) does not work if the document has a margin (i.e. width:1216px;margin:auto) - but I can work around this at the moment.
Anyway, the complete code is at http://www.geraldholdsworth.co.uk (it was easier to stick it there and post a link than to post the code here).