Abul Rahman has been taken into custody in connection with the photo which appeared during Ramazan period, Superintendent of Police P Mayilvahanan said.
However, Rahman told police that they did it to thank the ISIS for releasing Indian nurses from their captivity in strife-torn Iraq without harming them, the officer said. Rahman also said they had only shared their gratefulness and happiness over the release of the nurses as ISIS was not a banned outfit in India, Mayilvahanan added.
He said the 'Q' branch and Intelligence Bureau are investigating the incident. The photo was taken in front of a mosque at Thondi. Initial investigation revealed that the person who took the photo had gone abroad and uploaded the picture on a social networking site.
The t-shirts were made by a company at Kader Pettai in Tiruppur district in Tamil Nadu, he said, adding, in all 100 such t-shirts had been made and of them 36 were worn by the group.
Rahman's friend Villavan had arranged to make the t-shirts, he said. Police said the youths, who posed for the photo, did not have any links with any terrorist organisation, "but they are being monitored and have been warned severely."
"The mosque authorise had warned the youths against wearing such t-shirts. The youths had told them it was only a prank," an official of the Intelligence bureau said.
Officials said the picture had been withdrawn from the social networking site now. They also said they have not found any hardcore supporters of the ISIS in Tamil Nadu.