The talk started last week when LinkedIn announced it now has over 14 million members. The business professionals' network took advantage of the milestone to launch a new feature: the ability to add a professional photo to the online profile.

The move brings LinkedIn a step closer to the functionality of Facebook, which didn't make an official announcement this week but quietly launched a feature that at least indirectly competes with LinkedIn. Facebook now lets its members separate work friends from social friends.

Could a professional social network battle be brewing?

LinkedIn's Advantage

"Many of our members have requested to have professional photos added to LinkedIn profiles as a way to make the network even easier to use," Adam Nash, senior director of product for LinkedIn, said in a statement. LinkedIn figures many people can recognize and remember faces of colleagues and classmates more easily than names. LinkedIn lets users maintain control over whether their photo is visible to their connections.

"What LinkedIn has right now is the market share. I really do believe today people are using LinkedIn strictly for professional purposes and that the people are using Facebook for a mix of professional and personal purposes," said Jupiter Research analyst Barry Parr. "When I use LinkedIn, I get this sense that it's a system that's designed for a very specific purpose."

Indeed, LinkedIn is about professional networking. So it's not about just about connecting with people in your immediate network. It's also about connecting with people who know people you know, and maybe even people who know them.

Facebook, Parr said, focuses less on the broader network by forcing a consensual relationship between people who know each other. Of course, Facebook could decide to duplicate LinkedIn's architecture at any time.

Facebook's Advantage

Facebook might not need to, though. Facebook has its own set of advantages: a large, and quickly growing network of users; more than 43 million users to be exact. In addition, Facebook has formed relationships with developers to build applications for the site. However, analysts say Facebook has some disadvantages in comparison to LinkedIn.

"Most of the ways people use Facebook are really pretty trivial," Parr explained. "Facebook has some really cool and exciting networking features that let you do interesting things with people in your network, but they haven't reached the stage where people are using it for professional networking."

LinkedIn's long-term risk is that more people will begin using Facebook as a convenient way to communicate, Parr added. If Facebook users reach the point that they have more professional contacts in Facebook than in LinkedIn, the competitive advantage could tip in favor of Facebook. However, Parr said, "It's always difficult to unseat an incumbent and it doesn't happen quickly."