What you have here is a pretty tricky and untested legal situation. Let me try and give a rundown.

Generally, when dealing with matters of photography, the copyright rests in the hands of the one holding the camera, be it real or virtual. If I take a photo, even if it is of a model, I have copyright of the image (we won't get into misappropriation of image or privacy issues here). If I am under the employ of an agency, then it is a work for hire and they get the rights.

The exception is when you're taking a photograph of a copyrighted work. For example, if you took a photo of a painting that wasn't in the public domain, your photo would be a derivative work of the original and would be an infringement unto itself unless a fair use argument could be made.

If you do it with permission of the copyright holder, the original rightsholder still has copyright over the painting and you would have copyright over your photo apart from the painting.

So, in this type of situation, you have the potential for a work where two or more people have a copyright interest in a work. If we assume that the avatar is copyrighted, which is hard to say for a number of reasons and the photo was taken without permission, then the photos and all copies of it are violations of the original avatar. If avatar copyright is assumed and the photo is taken with permission, then the photographer holds the largest interest in the rights. If we don't assume avatar copyright, the photographer holds all of the rights.

This doesn't touch on an implied license, which might be assumed in a world such as second life and might allow photography of copyrighted works, nor does it look into the terms of service for participating in second life, which can say almost anything it wants on the topic.

If you have a headache, just imagine you're a judge trying to sort through these issues. This is why I don't become an attorney.

Anyway, I would encourage either the rightsholder or the avatar to file a complaint through Ebay's VeRO program. Failing that, consider filing DMCA notices against Ebay.

It certainly beats making this the test case for all of the above issues.

Hope that this helps clarify things (or not).