By day, Arvind Venkatraman works as a software engineer in India's tech hub Chennai. But in his spare time, he is an international art detective whose efforts have helped bring back some of his country's most valuable antiquities.

Venkatraman is part of a group of art enthusiasts known as the India Pride Project, who are using Facebook and other social media to identify religious artifacts stolen from temples around the country and secure their return.

Art theft is big business in India. But the richest pickings are in Venkatraman's home state of Tamil Nadu, where centuries-old religious artifacts with huge potential sale values in the West lie largely unprotected in out-of-the-way rural temples.