Complaints against a mobile billboard displaying a naked woman fingering a piece of melon in front of her pubic area have been upheld by the Advertising Standards Authority (ASA).

The billboard was produced by Eden Digital - formerly owned by porn tycoon Steve Crow - to promote the Erotica Expo. The billboard was driven around central Auckland, down Queen Street and around Britomart Place shortly after midday on a weekday in August.

The billboard featured a woman naked from the waist to her thighs with her fingers inside an open rockmelon strategically placed in front of her pelvic area.

"The image is designed to simulate a woman with her fingers in her vagina. It is standard Steve Crow fare, with its focus on dehumanising women and reducing them to their genitalia," complainant Denise Ritchie from the Stop Demand Foundation said.

About 70 other complainants voiced similar views.

The billboard was towed in and around Auckland a week before the expo was due to open so it was public and highly visible, the ASA said in its decision.

"It was clear that by using the naked female body part and the strategically positioned fruit and finger, the advertiser sought to provoke maximum outrage and receive maximum exposure."

The ASA complaints board was unanimous in the view that the advertisement was degrading to women and breached numerous basic principles of the Code of Ethics.

Advertiser Eden Digital said the complaints were the "same old same old puritanical nonsense" from a very small sample of the population, not even close to one per cent of those who would have viewed the billboard.

"At the end of the day the photo used on the billboard is nothing more than a naked woman holding a piece of fruit in front of her pelvic area. Whatever we do, someone will complain."