If the help does not support you, what you could do--might be a little tricky--is get the corrdinates of the img's location on the page, and copy those pixels from the bg, and just put that as the bg layer in the img with the overlapping layer set at 50%. However, I think that will only work if that page does not scroll.
I have been frustrated with this issue before, but I have no recollection of what I did to solve it!
