I understand that you want to plot some data using polarscatter and you wish to include a polar background image (after conversion from cartesian image).
In order to convert your Cartesian image to polar, you would first need to get the (x,y) co-ordinates of the cartesian image and then convert it to the (r,theta) form using "cart2pol" function. Then this image can be used as your background image for your scatter plot using the "imagesc" function.
