I have an account on Ebay and I haven't seen that particular picture, but I will keep searching for it. I must say that I am very disturbed at this development because I believe that your family should keep their Civil War historical photographs.
See if your mom can sign into her account and bring up past history of transactions. Don't know if they go back 4 years, but they go back pretty far. Also, does she remember the handle this Matt used in e-bay? If so she could look him up through the e-bay site. Other than that, can only wish you good luck.
No, I already checked their E-bay account and there is no info that far back. I also tried to see if they had given or received feedback so that I could see the e-bay I.D. of Matt, but, unfortunately, they only had one or two feedbacks that year, and none were for the picture.
OK - here's my last idea. 80% of e-bay transactions are done through Paypal. Ask her if this one was. I just checked my own Paypal account and it goes back to 1997. If so, have her go to her Paypal account summary and look for the link that says "View all account transactions". You'll have to play with the start and end date boxes, but it should be there.
If it wasn't through Paypal, it must have been a check. If so, have her check with her bank and see if she can get a copy of the check he sent.
I already thought of that and checked their Paypal but no luck. My mother was pretty sure it was paid with by check, but she was not sure and did not have any record of it, but is still checking to see if she can find anything. He might have paid with moneyorder though which would not leave a paper trail.