Web Bug

Web bug is a simple 1-pixel-by-1-pixel image tag that can be added to an HTML message. This image can be embedded into a web page or an email message to track users who have visited a landing page or opened an email. They are able to gather details about who is reading the web page or newsletter, when and from what computer. Web bugs are generally invisible to users, but are extremely valuable to online and email marketing success measurement. (Users may also refer to the small tracking images as a web beacon, tracking bug or pixel tag.)

Email marketers are able to add web bugs to newsletters and other messages sent out to their mailing lists. In emails, web bugs can note whether an email is read or if it was forwarded to other users. When email clients prepare to send emails with  these embedded tracking images, it will send a request to the receiving server for additional information. These requests encompass the IP address of the requesting computer, the time content was requested, the web browser that made the request and the existence of that server’s previously set cookies. This information is then associated with the web bug’s unique tracking token and stored on the server.

Spammers are also frequent users of web bugs, making email users leery of this tracking method. Again, these images help to determine which spam recipients open and read the messages before deleting them. Many email clients take steps to prevent this use of web bugs by turning off the HTML display in emails and only displaying the text (though users have the option to turn HTML display back on for trusted mailers) or by turning off the image display function while still allowing HTML to run any other functions.