Agreed with you posting above. That's why when the freelancer contacted the end client, he did not state, at that point, that they have infringed his copyrights. What he did is to inform the end client that the images they are using is taken by him and till that moment, he have not release any copyrights to anyone else yet. This being the case, he have put the end client on notice that the images they are using may have copyright usage infringement issues. And since they are the one using it, they may be pulled into this should this become a legal issue. In others words, the end client have been informed and should they chose to disregard this information, they do so at their own risk.
Another point to note here, copyrights may and will be transfered to a client base on the sales agreement/quotation/invoice. But till full payment is made, the sale is not considered complete ( payment being part of a sale ) and as such, unless other wise stated, the transfer of copyrights is also not complete as the transfer of copyrights, is part of the sale.
In simple term, if you have not paid for it, you don't own it, unless otherwise stated.