When I was looking at traffic numbers for the top photo sites this weekend, another stat caught my eye. Online photo editing site Picnik is also quickly climbing the ranks of photo sites from seemingly nowhere.

In January, according to comScore, the site attracted 6.6 million unique visitors worldwide, a tenfold increase from the year before. On comScore’s list of the largest photo sites, Picnik ranks No. 14, above Shutterfly and AOL Pictures, and just below Snapfish. Unlike those services, however, Picnik is not really a place people store their photos. Rather, it is a place where they touch them up and manipulate them before they post them on MySpace, Facebook, Flickr, Smugmug, or somewhere else.

Picnik is a powerful, cloud-based photo editor that is integrated directly into Flickr, SmugMug and other photo repositories. Competing online photo editors such as Fotoflexer and Photoshop.com (formerly and Photoshop Express) attract only a fraction as many users (1.4 million uniques for Fotoflexer and 760,000 for Photoshop.com.

I asked CEO Jonathon Sposato for more details. He offered that 45 million photos were uploaded in January, and that 45 percent of Picnik’s traffic is direct, 28 percent comes from search engine, and that only 18 percent comes from partner sites such as Flickr and Smugmug. Picnik offers a base version of its photo editor for free, and then tries to convert power users into paying a subscription for more features. While Sposato won’t get into the conversion rate of free to paid members, he says that the percentage is increasing, renewals are increasing as a percentage, and he says that Picnik is now cashflow positive, a little more than two years after launch.