I have had repeated issues with finding designs that I only uploaded to Amazon being sold on other third party websites. I believe this is happening because the thumbnail image urls on our Dashboards are not at all secure, are too high res and are not watermarked.
For instance here is a url to one of my designs below. This design is now being sold all over the damn internet. I can't report a DMCA violation because these websites completely ignore me and are probably not even in the US.
Amazon needs to do something about this. Security by obscurity does not work. Obviously the third party tools that Merch designers use like the Chrome plugin PrettyMerch know about these urls because they are able to pull the images.
I have tested this url after logging out of my Merch account and it still pulls the image, even in a new browser window. I texted it to a friend and he was able to open it also. At a minimum lower the resolution and add watermarks!