That clause is totally unenforceable. You can’t require them to provide extra photos to you at their expense to things they don’t own. Also, they likely didn’t read it that closely, don’t remember or don’t care because you can’t sue them for it. Hire a photographer or reach out to the photographers for the weddings you do (get a card at drop-off, etc) to get copies yourself. At best you can require that they sign off on using their likeness in advertisement/ portfolio building.