That's not true.
It's a chain of copyright. While the card company have overall copyright of the card's design and image, they then have to get permission from the original source (in this case LucasFilms). Likewise, someone taking a scan or photo of an item (in this case a trading card) are then copyright holders of that scan/photo.
Ebay photos are a funny case. The copyright agreement when you post an item for sale isn't the norm. Other users can use your photos within EBay, but only within EBay, unless you specifically express you do not want your images used by other users. This usage does not extend beyond EBay usage.
For further details on EBay read the full policy here: EBay Images / Text Policy
Technically all our scans are breach of copyright on the card companies. However, as there are millions of scans and it would appear no complaints or cease and desist cases are in action I think we are ok. There would be nothing stopping a trading card company from insisting all their cards be pulled from the database (unless there is a formal agreement in place with each of them). Let's just hope that doen't happen.
Regardless of all that, I've taken someone elses time, effort and usage of their property and used for my own ends. It simply seems courteous, polite and correct to give the credit in some form when asked for.