When you're using a background image, you need to tell Tableau, through your data set, where to plot the coordinates on the image. More on that here: Finding Background Image Coordinates | Tableau Software
Also, you can use this tool to create coordinates on an image: http://powertoolsfortableau.com/tools/drawing-tool
Hope this helps!
I have done what you describe below, but without success. Could we manage a quick remote session so I can show you my dilemma? This is show stopper for me
Tim Bourdois, CNE
Senior Business Consultant
Happy to hear that, Tim! If you could, please mark as answered. Thanks!