Web Beacons (sometimes known as web bugs, tracking pixels and clear GIFs) are tiny image files that allow a website to monitor your activity. They are often used in combination with cookies and can be inserted into an email for a similar purpose.
Web beacons are typically transparent 1×1 GIF images or 1×1 PNG images. They can be used for many purposes such as to track clicks on a link, to track traffic patterns, and to monitor user activities. They can also be used in email messages to track their delivery and receipt.
Web beacons do not send information from your computer back to the company that placed them on the website you visited. They simply allow websites to collect anonymous information about how visitors use their site, such as how long they spend there and what pages they view. The information collected by web beacons is then used by advertisers and marketers to better target their ads toward consumers who may be interested in their products or services.