Heavy users of digital cameras can end up with tens of thousands of photographs on their hard drives. And – given the difficulty of searching, organizing, captioning, and sharing large numbers of digital pictures – many of these images will never be seen again.

In 2004, Canadian startup Ludicorp started to fix that problem with its Flickr photoblogging website. Unlike commercial photo album services, like Snapfish and Kodak’s EasyShare Gallery, which are designed mainly to help people buy prints, Flickr (which is now owned by Yahoo) gave digital photographers simple Web tools for annotating specific areas of images, such as friends’ faces, and for labeling photos with searchable “tags” that make them easier for others to find (see “Tagging Is It”).

But Flickr’s features are still largely “manual.” Sharing photos on the site means sending friends new links every time you upload new images. Furthermore, tags must be typed in for each photo, and identifying Aunt Martha in photos from last year’s pool party still means drawing a box around her face in every shot and adding notes.

Now two new startups, BubbleShare and Riya, are providing Flickr-like photo-sharing services – but with impressive new features: audio-enhanced slide shows that can be embedded into any Web page, automatic downloading of new photos to friends’ PCs, and computerized face recognition and tagging.

BubbleShare made a splash several weeks ago with its initial product: an online system for building slide shows that can be viewed at its site or inserted into other sites, such as blogs (see “Building a Narrated Slide Show on the Web”). And today* BubbleShare introduced a beta version of the BubbleBar, which goes a step further, putting images directly on your – or your friends’ – desktop.

The BubbleBar pulls images from your online BubbleShare albums and sends a parade of thumbnails down the side of your computer’s desktop, like a filmstrip; placing your mouse over one of the thumbnails pulls up a larger version, along with captions and comments. But that’s not all. The BubbleBar also watches for new albums published on BubbleShare by your acquaintances and downloads them automatically. So, if your photographer friends are sufficiently prolific, you can wake up to a new set of images every day, without lifting a finger.

[*Addendum, 3/30, 6:50 pm EST: When the original version of this story went to press last night, BubbleShare had not yet launched the public beta of the BubbleBar. It did so today, along with several other new features such as the ability to vote on the best slide shows and add bubble-like captions to photographs. We have updated the story accordingly. --Eds.]

BubbleShare’s idea of automatically retrieving shared photos was inspired by Ceiva, whose digital photo frame has been on the market since 2000. Every night, the Ceiva frame connects via telephone to an online collection of photos uploaded by the owner or his friends and family. “We love what Ceiva does,” says BubbleShare CEO Albert Lai. “We wanted to bring that experience onto the desktop.”

Photo annotation and tagging is another tedious process that software is beginning to take over. Like Flickr or BubbleShare, Riya allows users to upload an unlimited number of photographs; the difference is that its software (released in beta on March 21) uses techniques derived from computer-vision studies to examine the images as they’re uploaded and pick out faces it has been trained to recognize. When these particular images appear on Riya’s site, the faces that the software identified are marked by a Flickr-like box and label.

In principle, a Riya user could upload an entire photo collection and allow the site’s face-recognition technology to categorize them according to the people who appear in them. Later on, it’s easier for a user to find old photos or for others to come across them in image searches.

In addition to faces, Riya’s software can read text that appears in photographs and use that information to create tags. For example, if you and your family appear in front of a sign for the Piccadilly Circus Underground station in London, Riya could automatically give the photo a “London” tag. In the future, according to the company, their software will also be able to recognize well-known objects, such as monuments.

Both BubbleShare and Riya offer free uploads and storage, and plan to earn revenues by publishing advertisements alongside user’s online photo albums. The specific ads that appear will be determined by a keyword-based advertising system similar to Google’s AdWords. In Riya’s case, the tags automatically derived from users’ photographs could be used as keywords – so that a photograph of the National Park Service’s “welcome” sign at Alcatraz, for example, might be accompanied by ads for ferry services in San Francisco Bay.

People will need more and more help as their digital photos pile up, says Ed Lee, a digital-photo analyst at research firm InfoTrends in Weymouth, MA. “The heavy [digital camera] users will have tens of thousands of images on their computers – and even the light users are probably still in the hundreds or low thousands,” he says. “I personally have about 15,000 photos that I’ve accumulated over six years. In the big scheme of things, it’s going to be really important to be able to find your photos wherever and whenever you want them, no matter where they’re located.”

Lee’s only concern about the latest crop of photo-sharing startups: How will they stay afloat financially, given that they aren’t charging fees, such as Flickr’s $24.95 annual subscription for an account that allows unlimited uploads? “There’s only so much money out there from advertising,” Lee says. “And only a small percentage of people – less than one-quarter – say they’re willing to pay some money for a premium-type photo service. There’s a market opportunity here, but where the money’s going to come from isn’t clear.”