Police Col. Worapong Thongpaiboon, of the Crimes against Children, Juveniles and Women Division, advised women not to get carried away if their boyfriends have a video camera or a mobile phone with built-in camera.
Videos or cameras are sometimes hidden in rooms, he added, and one way to tell is if the man keeps looking in one direction or suspiciously positions a woman in a certain direction.
Worapong, now called "the Hi5 detective," said spreading nude photos around may not be a serious crime, but each month four or five women file complaints with police over explicit pictures or videos taken of them without their knowledge.
''It is alarming. The victims come from all walks of life — high school students, civil servants, teachers, doctors, pharmacists, even corrections officers. Some victims are celebrities,'' Worapong said.
He said people who post nude photos on Hi5 are men taking revenge on women who had dumped them.
Worapong arrested a graduate student for posting nude photos of his former girlfriend on Hi5. The 23-year-old man admitted he posted 11 photos of his former girlfriend on the site to force her to meet him. She did meet with him, but insisted on leaving him, so he posted another three nude photos.
The student was charged with forcing the woman to act against her will and spreading pornographic images by computer. He is facing a maximum of three years in jail on the first charge and up to five years for the second charge.
''I cannot stop couples having sex. I can only warn them that by the time their nude photos are exposed on a public network, it is already too late,'' Worapong said.