Prior to 1975, to obtain an order for Divorce to terminate a marriage, the applicant had to prove that the other party had breached the marriage contract sufficiently for the Court to order that the marriage could be terminated.
The ground of Divorce was most commonly breach of the marriage contract by infidelity. To prove infidelity to the Court, the applicant was required to show evidence of an affair.
This resulted in private eyes pursuing photos of indiscretions for the applicant to show the Court.