This is easily solved.
Tell your buyer to copy and paste a picture from the original listing - one of your pictures.
Then they will be able to complete the return request.
Opening a case through Ebay protects the buyer and seller. There will be evidence on your account that you have dealt with the refund so the seller will not be able to open a chargeback later on.
The buyer is protected as Ebay will step in to refund them if tracking shows you have the item back but you don't refund them.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)