The check wasn't altered. The drawee bank had the right to return the check "not endorsed as drawn," but that would have had to be done by the midnight deadline.
The argument remaining is that the bank that cashed the check guaranteed the missing endorsement; i.e. that of the payee. The water is a bit murky on that point in light of the fact that the check was actually endorsed by someone else.
The claim against the bank that cashed the check can be made by either your customer or you, but it will be made outside the clearing system. The claim will reference 4-205(2) and be supported by an affidavit from the photographer that he or she did not get the proceeds.
It would be prudent to point out to the customer that the other bank may file charges against her son if they have to cough up the money...
In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.