I have several of my items doing the same thing. There is no solution within eBay for this. When you use their tool, it pretty much follows what the OP originally stated. If you try to delete the photo and upload another, eBay says you can not have more than one image from an outside host. I have not had much success in repairing the issue through eBay. This has been intermittent over the last year or so. Out of a couple of hundred listings a week, I get one or two that this happens. Not really too big of an issue in my eBay world. But might be for other sellers.