The massive rise in blogging has sparked an even bigger increase in traffic on photo-hosting web sites, with teenage girls the biggest users of the latter service, a research firm said Tuesday.

Since the beginning of the year, traffic on image-hosting sites overall has shot up 406 percent to more than 14.7 million unique users, Nielsen/NetRatings said. The number of people using the sites represents 10 percent of the total U.S. Internet population.

The top referring sites for the top 5 photo-hosting sites were blog-hosting service providers MySpace.com, Xnga.com, LiveJournal, Blogger and Microsoft's MSN Spaces, the research firm said.

In July, 29.3 million people, or 20 percent of active U.S. web users, accessed blogging or blog-related sites. That number represented a 31 percent increase since the beginning of the year.

Nielsen analyst Jon Gibs said blogging has lifted traffic on other web sites, but none more than on image-hosting sites.

"Simple text-based diaries (blogs) have evolved into a more image-oriented presentation," Gibs said in a statement.

Nielsen analyst Jon Gibs said blogging has lifted traffic on other web sites, but none more than on image-hosting sites, which have been caught up in the trend of having more photos on blogs.

Girls between the ages of 12 and 17 were the biggest users of photo sites, accounting for 15 percent of the total number of users, Nielsen reported. Teenage girls were two-and-a-half times more likely to visit an image-hosting site than the average user.

"It's not that incredibly surprising," Gibs said of the use of photo sites by teenagers, who have been quick adopters of the "fun element of blogging."

To some extent, teens are copying celebrity-magazine photos that are surrounded by text giving a description of what's shown, Gibs said. Many teens post pictures of places they've been, as well as of themselves and friends.

"Teens are much more interested in personalizing images by commenting on them," Gibs said. "It's a way of expressing their view of the world."

The teens' behavior is a reflection of a general movement among Internet businesses to provide customers with a more customizable and personalized experience online, Gibs said.

Boys between the ages of 12 and 17 were second to girls, accounting for 10 percent of the total number of users. Young men between the ages of 18 to 24 were third with 7 percent.

Young people have created millions of social circles online, and Web journals have become "just another way of getting to know someone," Gibs said.

The top image-hosting site in terms of traffic since January was PhotoBucket, followed, in order, by ImageShack, Putfile.com, TinyPic.com and Imagevenue. The latter three sites launched this year.

In other Nielsen research, Yahoo Inc. had the most traffic in August with 101.3 million unique visitors, followed, in order, by Microsoft, 95.6 million; MSN, 92.1 million; Google Inc., 80.4 million; and America Online Inc., 75.7 million.

In ranking the combined traffic on all the sites owned by a particular company, Microsoft was first with 111.2 million visitors, followed by Time Warner Inc., 103 million; Yahoo, 101.5 million; Google, 81.7 million; and EBay Inc., 57.8 million.

United Online Inc. led in online advertising revenue, followed, in order, by LowerMyBills.com Inc., Vonage Holdings Corp., Apollo Group Inc. and Dell Computer Corp.

The advertiser rankings are based only on revenue from the cost per thousand impressions, or CPM, which is commonly used for banner ads. The rankings, for example, do not include search-based advertising.