Flickr, Yahoo's (NASDAQ: YHOO) popular photo-sharing site, announced yesterday that subscribing users will be able to upload and share short-form video content.

"Adding the ability to share videos on Flickr is a natural extension of our mission to be the 'eyes of the world' -- letting our members share what they see with the people who matter most to them, be they family and friends, or the world," Flickr General Manager Kakul Srivastava wrote in the Yahoo company blog.

The announcement comes as the volume of video content on the Web is growing rapidly, and content publishers are probing new models of distribution and monetization. In January, U.S. Internet users watched 9.8 billion videos online, a 35 percent increase from the same time the previous year. One-third of those videos were seen on Google's YouTube.

While the comparisons to YouTube are inescapable, video on Flickr differs in a number of important ways.

Flickr is limiting the length of video clips to 90 seconds and the file size to 150MG, whereas YouTube sets the cap at 10 minutes, and supports files as large as 1GB. Srivastava said that most video clips are essentially "long photos" of the poignant moments of daily life that people record on their digital camera or cell phone.

"We think 90 seconds is a really comfortable limit for what the feature is designed for, which is capturing those moments," said Terrell Karlsten, a spokeswoman for Yahoo.

That view finds support in a recent online video study conducted by JupiterResearch, which found that despite the increasing availability of full-length TV shows and movies on the Web, short-form videos remain the most popular format.

Karlsten said that Flickr would respond to user feedback as people start exploring the video feature, and that it might consider expanding the length and file-size limits if the demand was evident.

At present, only paying subscribers can upload videos. A Flickr Pro Account provides unlimited uploads, storage and bandwidth, at a cost of $24.95 a year.

Unlike YouTube, there will be no advertising on Flickr videos, at least at first. Karlsten said that the business model is built around paid subscriptions, but that Flickr would consider expanding the ability to upload videos to all users in the future. In that case, ads would likely appear in Flickr videos just as the site currently tags ads to photos submitted by non-paying users.

Karlsten said that Flickr is committed to its roots as a community-oriented site, so there will be no content partnerships with professional publishers, such as movie studios, which routinely promote coming attractions with trailers on YouTube.

"It's designed for the personal and authentic videos that people are capturing on their digital cameras," Karlsten said.

Flickr said that it will remove any unlicensed content that appears on the site, and issue a warning to the user who posted it.

Users will be able to upload videos into their photostream, and apply the same tagging features that they currently use for photos.

For all of the differentiators from YouTube, it is difficult not to imagine Flickr the video service as a potential competitor. On comScore's list of the most popular video properties on the Web, Yahoo sites ranked third behind Google's sites and those of Fox Interactive Media (FIM), whose video viewership is largely driven by MySpace. But while YouTube gave Google a 34 percent market share, FIM only served 6 percent of online videos, while Yahoo checked in at 3 percent.

Fourth on the list is Microsoft, which, of course, is trying to acquire Yahoo to narrow the advertising gap with Google. For its part, Google has recently been talking about its plans to ramp of the ad revenue brought in by YouTube.

Certainly its community focus is a key part of Flickr's success, but from a competitive perspective, it will be hard to keep the video portion of the site ad-free and without professional content as Google turns up the dial on monetizing YouTube. The fate of Flickr will be an interesting one to watch should Microsoft succeed in its takeover bid.