Whenever a user opens a page with a graphic browser or email reader, such image and other information is downloaded.
This download requires the browser to send a request to the server storing that image or information, allowing the organization running that server to keep track of the HTML page.
In this way, the sender can gather detailed information about when and where each particular recipient reads email.
Every subsequent time the email message is displayed can also send information back to the sender.
Originally, a web beacon was a small (usually pixel transparent) GIF or PNG image (or an image of the same color as the background) that was embedded in an HTML page, usually a page on the web or the content of an email.
Modern web beacons also use the HTML IFRAME, style, script, input link, embed, object, and other tags to track usage.
Whenever the user reads the email, the image at this URL is requested.The server can store all of this information, and associate it with a unique tracking token attached to the content request.Web bugs are typically used by third parties to monitor the activity of customers at a site.The part of the URL after the question mark is ignored by the server for the purpose of determining which file to send, but the complete URL is stored in the server's log file. Using this system, a spammer or email marketer can send similar emails to a large number of addresses to check which ones are valid and read by the users.Web beacons can be used in combination with HTTP cookies like any other object transferred using the HTTP protocol.