A hotlink is a direct link in an HTML file to a file on another server. While there are some legitimate uses for hotlinks, in many cases they are a source of irritation, because they can sap bandwidth in addition to violating copyright laws or placing media out of context. Images are most commonly hotlinked, along with audio and video files. There are a number of ways to combat unwanted hotlinks if you have noticed a drain on your bandwidth which you suspect is related to hotlinking.
To understand hotlinking a little better, look at the image to the left of this article. This image is stored on the wiseGEEK server, and if you viewed the source for this page, you could find its location. If you displayed this image on your own web page by linking to the wiseGEEK location, wiseGEEK would pay for the bandwidth used every time the photograph loaded. Unfortunately for the would-be hotlinker to wiseGEEK images, wiseGEEK has protections in place on its servers to prevent hotlinking, but you get the general idea.
Tracking hotlinking is generally easy to do for website owners who keep track of their site statistics. If you notice a sudden spike in bandwidth usage, you may want to check your site access logs to see if people are accessing a specific file repeatedly, which suggests hotlinking. Most hosting providers offer several tracking services to help their clients monitor bandwidth usage.
There are some legitimate reasons to use a hotlink. Some people have multiple websites, for example, and they may want to display content stored on one server on another site. Many advertisement programs also use hotlinks to place their material on client pages. Sites like Flickr and YouTube allow users to hotlink to material stored on their servers so that people can embed videos and photographs on their websites. However, many hotlinks are not legitimate, in which case hotlinking can be called piggy-backing, sapping, or leeching, in a reference to the bandwidth used up by hotlinking.
In the sense of general Internet etiquette, a hotlink is not polite because it steals someone else's bandwidth. For photographers and other creative professionals, hotlinks are irritating because many people use them to pass off creative material as their own, or to display such material out of context. In some cases, a hotlink can result in a copyright suit. Many site owners understand that people hotlink out of ignorance more than malice, and they generally send polite requests to stop hotlinking before they take more aggressive action.
There are a number of responses to hotlinking, ranging from juvenile image switcharoos to installing hotlink protections on servers. In the case of a switcharoo, an irritated website owner might replace the original image with an offensive, humorous, or out of context image to alert the hotlinker to his or her error. Many hosting companies also provide hotlink support in the form of code which will deny hotlinking requests; this service is generally not available with free or low cost hosting, although you can always check.
Using server protections will not prevent people from stealing material from your site by downloading it and then hosting it on their own servers. Many photographers like to watermark their images to make theft less appealing. If you see an image you like, ask the person who owns it if it is OK to use the image. Many people are happy to allow you to use their work, as long as you give the artist credit and download the image to your hard drive before uploading it to a server you pay for, or to a free file sharing service like Flickr. You can also use a service like Creative Commons to search for media which you can freely use, modify, and share.