With more than three billion images, Flickr is probably now the main repository for photos on the Web. Photographers use the streams to show their works to each other, the groups to swap ideas and learn how to improve their skills, and the site’s networking to make new friends and build contacts.

that it is not commercial, it’s also used by buyers and photo editors looking for unique images for their books, magazines, websites and for advertising. Some of the deals made between commercial users and amateur Flickr contributors include a billboard commission for Toyota, photos used on book covers, images used in Microsoft’s Vista and plenty of commissions for magazines.

Clearly, the competition is going to be intense. But because few photographers on Flickr really understand how to market themselves, a little bit of care can go a very long way towards standing out on the site and putting your images in front of buyers.

As always, you’ll need to shoot good quality images, of course, but here again, it really helps to shoot unique images.

There are—literally—tens of millions of photographs of cats, dogs and other animals on Flickr. A quick look at Flickr’s tag cloud will show you the most popular topics on the site, and therefore the subjects to avoid if you want your photographs to stand out.

As is so often the case, you’ll do much better by focusing on a specialization and keywording those images carefully.

It doesn’t have to be the only subject you shoot for Flickr—you can have different sets or collections for different topics—but you do want to make it as easy as possible for a photo buyer looking for images of butterflies, for example, or interior design to find you and your portfolio.

Flickr is one of the few sites that can be said to have changed the way commercial photography works. The huge number of images on the site make it rich pickings for photo users looking for the kind of photos that they won’t see offered by stock companies.

Those buyers don’t care that the photographer they’re dealing with is not a professional—in fact, when it comes to the negotiations, that might even be an advantage—what they really want to know is whether the picture is good enough to do the job.

But Flickr doesn’t make it easy for users to track down contributors. The search function isn’t very detailed, too many photographers upload every image they own to the site so that the best shots get buried and few make proper use of sets and collections.

If you can organize your images properly and network to make sure that people know where to find them, landing sales should just be a matter of time.

Flickr is free to join and sign up takes just minutes. It is however, worth paying the $24.95 annual fee for Pro membership.

This doesn’t just give you additional storage space and better organization features—worth paying for alone—it also gives you stats, and they can be very valuable indeed.

Your Flickr stats will tell you which images have generated the most views and the most comments. Most importantly, they will also tell how people reached those images and what keywords they used to find them. That’s the sort of information that can help you to target your photo stream to pick up more viewers.

Keywording based on information gleaned from the stats isn’t the only way to market your Flickr stream though. There are a number of other strategies that are at least as important.

Networking is a vital element in Flickr marketing. The more people that know you’re on the site, the greater the number of views, faves and comments you’ll receive and the larger your contact list will become. Networking can be carried out by being active in groups but it’s also done by leaving comments at the bottom of other photographers’ photos. When you leave an interesting comment, the photographer is likely to leave you one in return.

Each day, Flickr highlights the most popular images on the site. Appearing on the Explore page sends views through the roof but the choice of image is made automatically, based on an algorithm that considers a combination of views, faves and comments. It also takes into account the number of groups that an image has been submitted to, penalizing images entered into more than fifteen to twenty groups.

Keywording, networking and promoting particular images to build views and hit the Explore page all target users already on Flickr. But it’s also important to bring in users from outside the site.

Even something as simple as including your Flickr URL on your Moo cards and email signatures can help to increase views—and the chances of making a sale.

Starting with Flickr is easy. Just sign up at flickr.com. It’s stopping that’s hard. Sign up at the site, create sets and collections and begin uploading your images and networking with other photographers.

You can then start playing. Try geotagging to help people looking for images of locations find your photos, and place Creative Commons licenses on some of your lower-quality images. That will attract people looking for free photos. You can then offer them better versions for a fee.

Be Selective

Your Flickr stream needs to be seen as a portfolio rather than a dumping ground for all of your images. Create sets and collections for easy browsing and only show your best work in each category. If a buyer wants to see more, he can contact you, but show your skill not every image you’ve ever taken.

Use the Descriptions and Bio

You can add descriptions to your images and write a bio page too. Your descriptions tell potential buyers what they’re looking at but you can also add a line indicating that the photo is available for licensing or for sale as a print. That will show buyers that you understand the commercial side of photography and you’re willing to make a deal.

Your bio page too is really a sales page. Keep it brief but explain what you shoot and how you shoot it, and include a link to your website so that buyers can pass through, see more of what you have to offer and place orders.

Make the Comments Worth Reading

Commenting is an important part of networking but comments that say little more than “great capture” are worth nothing. Explain why the image is good, point to similar images the photographer might like to see and offer tips that could help her make it even better. Make your comments worth reading and you’ll make your images worth looking at.