SAN FRANCISCO—According to leading web experts, a photo of an unidentified naked woman has caused an online sensation after appearing on the Internet sometime last week.

The inexplicably popular photograph, which features the woman exposing both breasts as well as providing an unobstructed view of her vagina, has been visited an estimated 750,000 times since it was first discovered two months ago.

The popularity of "Subject X," as the naked lady is known in academic circles, has baffled researchers.

"For some reason, people cannot seem to get enough of the naked woman picture," said Michael Vianna, a web analyst for Comstar Market Research who has been closely following the trend. "Though the image displays no discernible function or real-world application, it continues to enjoy immense popularity with Internet users. It is utterly perplexing."

Vianna, who closely examined the photograph over several days in an attempt to understand its appeal, said that the nude-lady photo falls completely outside typical uses for the Internet, like checking e-mail or accessing helpful information such as tax laws and driving directions. Even more unusual, the photo contains no information regarding the woman's acting or modeling career, her possible relevance to American history, or name.

"This image contains no encrypted data or practical content of any kind," Vianna said. "Even more baffling is that, in terms of web traffic, this seemingly pointless image has vastly surpassed websites as informative and indispensable as WebMD.com and Yahoo! News."

"If only she were wearing a T-shirt with some slogan on it or standing in front of a national monument, perhaps then we could begin to understand this enigmatic image," Vianna continued. "In the end, however, it is simply a picture of an unclothed female approximately 20 to 30 years of age posed with her breasts and vagina clearly visible."

According to Vianna's research, there are no significant patterns relating to the viewing behavior of those accessing the picture except that the majority of the traffic usually comes late at night. And, though web-usage reports indicate that the naked woman picture interests people of all ages, income brackets, and ethnic backgrounds, there is no evidence that the photo has ever been shared with viewers' family members or coworkers, or featured in a CNN.com photojournalism slide show.

"It appears as if every one of yesterday's 27,430 viewers accessed this specific portrait independently of one another, and may even have searched for it intentionally," Vianna said. "What could have driven them all to seek out this particular photo of an anonymous, undressed woman? We may never know."

The unaccountable popularity of outwardly useless Internet content such as the naked woman picture is not unheard of. According to freelance web consultant Joseph Ziarko, these Internet "memes" are difficult to explain, as there are no factors to dictate why something as nonfunctional as a 6 x 9" digital capture of a well-endowed, tan-skinned woman lightly moistened by either sweat or beach water would interest so many people.

"No one really understands why these things catch on," Ziarko said. "Like the Hamster Dance website from a few years back or the recent interest in LOLCats, there is some intangible quality about this photo that thousands of otherwise-normal people find captivating. Maybe the fact that it is in such sharp focus."

Though interest in the photo currently remains high, Ziarko predicted that the Internet-using public will soon tire of the naked woman picture once the web is saturated with images from imitators attempting to duplicate its popularity.

"By next month, the Internet could be home to literally hundreds of pictures of naked women," Ziarko said. "There's simply no way the trend can sustain itself. People will very quickly get bored with the constant barrage of bare breasts and vaginas."

Many experts agree with Ziarko, but others in the field have suggested that the picture could spark a lucrative industry in which images of naked women are licensed to decorate promotional gas-station soda cups.