A 55-year-old man in Tokyo has been arrested for allegedly aiding in displays of child pornography images through a smartphone app.

Mitsuaki Ono, president of Aircast, who lives in Ota Ward, is suspected of helping teens post pornographic images of themselves through the firm's picture- and video-sharing app titled Shashinbukuro (roughly translated as photo bags).

It is the first time police have taken action against operators of image-sharing apps for alleged violation of laws against prostitution and child pornography.

According to the Metropolitan Police Department, cases of teens posting images of themselves on smartphone apps for money are surging, and some underage girls have gotten into trouble.

Ono has denied any wrongdoing, investigators said.

Users of Shashinbukuro can set up passwords as they post images online, with the option of charging money for them. The passwords are posted on Internet bulletin boards and can be viewed by anyone, investigators said.

A total of 4 million people have used the app, and the firm is believed to have raked in ¥150 million in profit between November 2013 and July.

The MPD and Kyoto Prefectural Police had raided the office of Aircast in Chiyoda Ward in June.