India, Sept. 20 -- Fiction has made detective work look simple. Sherlock Holmes followed a clue wherever it led. Hercule Poirot rebuilt a crime from details that seemed insignificant. Neither had to answer the questions that constrain a real investigator: Is the surveillance legal? Who authorised it?

These questions came up at the Supreme Court's July 31 judgment in Himanshu Chordia vs State of Rajasthan, where a bench of justices Sanjay Karol and Vipul M Pancholi examined material that purportedly showed a woman pursuing a relationship outside her marriage. The appellant had placed roughly 237 photographs and 92 videos before a trial court.

The bench, suspecting that the images and videos may have been procured through private investig...