In a rare form of protest in China, supporters of dissident artist Ai Weiwei, under investigation on pornograhy charges, are posting nude photos of themselves.

They are using a Web site that proclaims: Ai Weiwei Fans' Nudity.  Listen, Chinese Government: Nudity is not Pornography.

Beijing police questioned Ai's videographer on Thursday, for allegedly spreading pornography online by taking nude photographs of Ai and four women. One of the pictures, One Tiger Eight Breasts, shows Ai posing nude on a wooden chair, flanked by four naked women who are giggling and smiling. The room is bare, the Chinese-style chairs are hard and the overall impression is sparse.

This is not pornography. If they see nudity as pornography, then China is still in the Qing Dynasty, which was overthrown 100 years ago, Ai wrote on Twitter

The investigation comes days after Ai was forced to pay a fine to the government over a tax bill. Ai had been held for 81 days at a secret location, where he was reportedly questioned about subversion, accused of tax evasion and given a fine of 15 million yuan. Ai paid a bond of 8.45 million yuan (US$1.3 million). The money was raised from supporters across China, with some throwing cash into the courtyard of his Beijing home.

Many of his assistants have been detained for lengthy periods and interrogated about Ai's political beliefs, business and personal life.