Sites such as Flickr have created whole communities of both professional and amateur snappers, and users can link to and comment on each others’ images.

We’ll be looking at the major sites, what they have to offer, and how to get involved. Whether you’re a viewer or a picture taker, it’s a simple matter of getting online and getting started.

Broadly speaking, the available photo-sharing services are split into two groups. The first group is familiar to many readers – their purpose is to sell prints of users’ photographs, either onto paper or other goods such as mouse mats, T-shirts or mugs.

The second group is more about sharing the images online, and making it easier to view them. While these sites sometimes include printing services, that’s not the main reason they’re there.

In the first instance there are sites such as the Kodak Gallery , Snapfish and Photobox . While these offer plenty of printing options, the sharing side is limited. Users can’t easily link to each others’ images, and restrictions are placed on use. Also, some of the sites require a purchase every so often to keep your account going.

Users who only want to share a few pictures with friends and family may find these sites handy, especially since they often enable viewers to order prints directly.

For those of us who want our photos to be seen by the rest of the world – or just friends and family – the second category of sites includes by far the biggest name, Flickr, as well as smaller sites Zoomr , 23 and Picasa .

What these sites share is a community focus – so users are encouraged to make their images public for viewing, and to get involved with commenting on other people’s pictures. They work well with blogs and other people’s websites.

All the services offer the ability to restrict photos to a select few – for instance, not everyone wants their children's baby pictures to be viewed by the whole world. Any friends or family who sign up can be added to your list as either Friend or Family, and will be able to see the pictures, which can be ‘tagged’ so they are restricted to either or both categories.

This brings us to the next innovation of Flickr: tagging. Photos can be tagged with words and phrases relevant to the image. Users are able to search for these tags and see the images.

So a picture of the Eiffel Tower at night might be tagged with ‘Paris, France, Eiffel Tower’ and ‘Night’, for instance. It’s up to each user what tags they use, and there’s no obligation to tag anything. Photos can also be arranged into sets, which make it easier to organise them.

All the sharing services encourage users to comment on each others’ photos, and pictures can be marked as favourites, so if a particular image appeals, it’s easy to find it later. Most of the sites have groups and pools, which feature users contributing to a joint gallery – any photos you tag with the name of the pool or group will be included, in some cases.

23 has a clever section called Stories, in which pictures can be joined up to form a narrative. Zoomr, on the other hand, concentrates on the local aspect, so it has special editions for various countries, and all pictures can be ‘geo-tagged’ which means that users can click on a built-in map to show others where the photo was taken. Flickr also features mapping abilities.

There are limits to the amounts that can be stored. The smaller 23 lets free users upload 30 pictures per month, and Flickr has a limit of 100MB per month (about 60 average snaps). Most of the free services will be suitable for casual users, but anyone who wants to upload more can upgrade to the premium version of each.

For 23, this costs €20 per year (£13), while Flickr charges $25 (£14) annually for a Pro account. Picasa offers 25MB of photos for free, with 6GB for $25 (£14) per year, and much higher charges for larger limits.

Both Flickr and Picasa offer easy-to-use tools for uploading pictures to the site, and all of them allow uploading via their sites. Some even enable users to email pictures in.

Flickr’s ‘Uploadr’ is a free download, and pictures can be dragged and dropped into its window. From there it’s possible to rotate them and sort them into sets for the website as well as tagging them. However, it doesn’t allow editing, so it’s necessary to have a separate photo-editing program.

To download Picasa, go to http://picasa.google.com , click on Download Picasa and run the file that is downloaded. Follow the prompts to install the program. Make sure the ‘Run Picasa’ box is ticked. The program will prompt to scan the computer for images – tell it whether to scan the whole thing or just the Documents folders.

Unlike the Flickr program, Picasa includes editing facilities. Double-click a photo to see the edit screen. There are buttons to auto-fix common problems on the left, and tools such as a screensaver creator and poster and collage maker in the menus. Once you’ve finished editing, click Back To Library. Make sure you click Save Changes on the main screen to save all the edits.

To upload an image, click the Web Album button at the bottom. The first time, it’s necessary to sign in – click on ‘Sign up for Web Albums’ and enter your Google account details if you have one. Otherwise click ‘Create a new Google Account’ and follow the prompts. Then enter your details into the Picasa window and click Sign In.

When digital cameras first arrived they revolutionised the way we took pictures – many of us now carry a camera as a matter of course to places we wouldn’t previously have thought of taking them.

It has taken a few years, but photo-sharing sites are about to change how we store and share our pictures. They are available to friends and family as before, but as well as that the whole world can get in on the act.

First, there’s the question of backup. If you upload all your pictures to a site, they can be retrieved if the computer loses them. Watch out, though, the site may not be storing the original, high-quality version but a smaller, compressed image. That means you’ll need a separate backup of the originals.

The second meaning concerns personal safety – how do we know our pictures won’t be used by criminals or, for instance, stalkers? If your images are public there’s obviously no way to stop people viewing them. But avoid giving away your location or details about your home, and make sure sensitive photos, such as baby pictures, are marked as viewable by friends and family only.

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