@lorro, I think you have misunderstood my problem.
I am able to add my own (Transparent Background) images OK. But they are just overlaid over the woocommerce placeholder. The Placeholder image is therefore visible through my transparent background.
Here is an example. https://catsails887161714.blog/?product_cat=no-3-rig-onemetre
I therefore need to remove the default Woocommerce placeholder image so that it is my page background that is visible through the transparent background of my image