Since the advent of graphical Web browsing, photography has had a big Web presence. Digital cameras make it easier than ever to create digital photos that can be uploaded to the Web.

Many people, however, use the photos they find at other Web sites. They may use them for their own Web sites, for school projects, or even for offline for-profit business purposes.

In most cases, such use is, in plain language, illegal. Using the photos that others took without their permission is copyright infringement, unless those owning the photos have made them available to the public domain.

The mistake that many make is believing that if a photo is on the Web, it's in the public domain and free for the taking. The reality is that any time a piece of intellectual property, including a photo, is created in a tangible form, it's automatically copyrighted, which grants the creator rights over how it's used.

A photo or other piece of intellectual property doesn't need to be accompanied by a copyright symbol (a "c" within a circle) to have copyright protection. This has been true in the U.S. since the country signed the international Berne Convention in 1989.

Trampling on a photographer's legal rights can get you in legal trouble. As attorney Andrew D. Epstein points out at his Photo Law Web site (www.photolaw.net), "The Copyright Act provides stiff penalties for infringing copyrighted works. Under appropriate circumstances, penalties can include monetary damages, all profits earned by the infringer from the unauthorized use of the copyrighted work, and attorney's fees."

Typically, infringers get a scary-sounding cease-and-desist letter from a lawyer. But photo infringers have been sued for damages. In "Diary of a Copyright Infringement Lawsuit" (http://www.photoattorney.com/?cat=21), Carolyn E. Wright, who calls herself "the Photo Attorney," spells out the procedure in filing such a suit.

Fortunately, there are easy ways to avoid this kind of legal messiness. One way is simply to get permission from the person who took the photo to use it. Often, if your purposes are educational or nonprofit, there's no cost. Sometimes, however, you need to pay for a license.

Another way to legally use the photos of others for free or for low cost is to use a photo whose creator has deliberately released it into the public domain or who charges little. Just as some computer programmers create programs they allow others to use for free (freeware) or ask for donations (shareware), there are photographers who take pictures for others to use for free or low cost.

The following sites, which provide search tools to help you find the type of image you're looking for, all come highly recommended:

Stock.xchng (www.sxc.hu) is a good site if you don't even want to think about paying for photos and still be legal. It includes about 400,000 photos, with about 2.5 million registered users since it launched in 2001. The site actively encourages users to share not only their photos but also their personal profile and their thoughts, with online forums where participants can comment on and critique each others' work.

Flickr (www.flickr.com), which is primarily a photo and video hosting site, has two areas where you can obtain photos for free. "The "Commons" provides photos from museums, libraries, and other institutions. "Creative Commons" includes photos from users who agree to make their work available to others under various conditions, such as use with credit to the photographer or noncommercial use.

Dreamstime (www.dreamstime.com) is primarily a commercial stock photo agency, with illustrations available as well. It has an inventory of more than 11 million photos that can be had for as little as 20 cents an image, depending on the subscription plan. But the site also has an area where photographers make their work available for free to achieve exposure and attract paying customers.

Bigstock (www.bigstockphoto.com) offers more than 4 million photos and illustrations to choose from. Its "credit packages" start at $15, which in this case gets you between one and five images, depending on their size, whether small for the Web or medium, large, or extra large for print.

CrystalGraphics (www.crystalgraphics.com) offers not only photos but Web site templates, Flash animations, and 3D graphics as well as special effects for PowerPoint presentations. One plan provides an annual subscription for $99 that lets you use up to 100 professionally taken photos out of its inventory of more than a million photos.

One last option, sometimes the only way to obtain the exact photo you want, is to take it yourself.