Legal Question in Consumer Law in California

That is a store policy issue, not a legal one. Under the law, sellers of goods are not required to accept returns at all.

If the store is smart, and most are, they won't. You could theoretically return an item with the photocopy, shoplift an identical item, and then return the stolen item with the original receipt. People run scams like this all the time. On the other hand, the store might accept the photocopy because the transaction number is on the receipt and their computers won't let someone use the same transaction number twice. But it's Highly Doubtful.