Hi there,
Understood the requirements. This can be done using ebay API. I would code a PH script that retrieves a list of all the products you have listed on ebay, and for each of them call the ReviseItem, replacing the picture URL.
I have 2 questions:
1) do you products have variations? If yes we'll need to take care of those too I believe
2) do some of your products have more than one image? If yes, then I guess I will have to retrieve a list of images for each product before doing any update, and then revise all images found, for all products
I have worked with ebay API before, didn't update photos but I am confident I would find my way without issues, since ebay's API documentation is clear and easy to follow.
I hope you would be able to test with me, at least once we reach the point we're ready to fire the first test run. I guess it will be best stopping the loop after 1 product and making sure the update went as expected for that one product, and once it does, then allow the script to do the full loop, hopefully updating all the image URLs within a few seconds.
Regards,
Julijan