Further to this, and what has turned out to be the best solution for what I needed to do - in the More Options section of each Product there are 4 custom fields, 'Custom 1:' through to 4 which can be called in the layout using the tags {tag_custom1} through to 4. If the Product has been assigned anything in these custom forms the page will display it and display nothing if there is nothing to display = perfect for my needs (don't have to create any place-holding image or whatever for every other product).
Hope that helps anybody else looking for this info.
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