When you put images on-line, your hope is that people will come to see them. To draw an audience you normally send out e-mails to everyone you think might be interested. But what if they like what they see, how do you bring them back each time you post new photos? One way to do so is by letting them subscribe to your photo album or blog so they are automatically notified when you post new photos. This not only saves you and your viewers time, it will likely increase how often your photos are seen.

If you have an iPod you may already be familiar with Podcasts. A Web site such as Wired posts audiovisual clips on-line so you can use iTunes to subscribe to the content they offer. When Wired posts any new Podcasts, iTunes lists them and when you connect your iPod they are copied to it so you can listen to them later.

The technology that makes this possible is called RSS (Real Simple Syndication), one of the standards that defines the "plumbing" for the process. (The other standard is Atom). For the process to work, both the sending and receiving end must have software that complies with the same standard. The sending end is called a syndicator and the receiving end a reader. At different times, you may find yourself a syndicator or a reader.

• The syndicator. The syndicator is generally a photo sharing site that supports RSS and lets you tag photos or put them into an album that others can subscribe to. Some sites let you choose between RSS or Atom formatted Web feeds; others offer only RSS or only Atom.
• The reader. At the reader's end things can get a little more complicated because there are all kinds of readers (also called aggregators). Each reader has its own design, but all help you find, subscribe and unsubscribe, and read or view feeds. We've already mentioned iTunes, but readers are also included in most new browsers, or can be added to them, and are built into sites such as My Yahoo! and Google. They are even being added to digital picture frames so you can feed them pictures from anywhere in the world. Mobile phones and TiVo video recorders also incorporate readers. Up-to-date readers support all forms of RSS and Atom feeds.

An orange logo is often used to link to public RSS feeds. Until recently there was a variety of logos, some reading XML or RSS. There is now an attempt to standardize on one design. In most Web browsers, you can click the logo, but at times you have to right-click it and then copy and paste the link into your news reader.

The Apple version of RSS for photos is called Photocasting. Using iPhoto 6 or later, you place the photos you want to share in an album on your computer. You then click the Photocast this Album button and iPhoto publishes the album on .mac so others can subscribe to it by clicking a link in an e-mail you send them. When they subscribe, the full-resolution photos are automatically downloaded into an album in their iPhoto 6 library. From there the subscriber can make an iPhoto book, calendar, cards, slide show or use the images in a screen saver or as a desktop image. Whenever you add photos to the album they appear in the subscriber's album automatically. PC users can subscribe to your Photocasts using any RSS-compatible browser or RSS reader.