Good Morning Sunshine (hmmm... should that be to music?)
If you have an image editing program, it should allow you to type text (your eBay user ID) on top of the image. If you have the feature, you can also change the text opacity so that the text appears but does not obscure the image below (see item #120036189460). Typing text on an image that does not touch onto the item itself is pointless - the thieves will merely crop out your name and the image will still be available for their use.
Keep in mind that some thieves care little that your name appears on the image. Your name should simply make it easier for eBay to verify your claim that the image is yours.
The real fun is when you catch someone directly linking to your images on your own picture hosting. It involves swapping out the image name with a new image that makes it clear that the person is a thief. The new image will automatically appear in the thief's listing telling anyone who views the listing what a lowlife they are.
Hope that helps.
Bill
treasure-pot
Bill
