Also known as "web bugs", "clear GIFs", "tracking pixels", "invisible GIFs", "pixel tags", or even "spyware" (because they record online activity), web beacons are transparent graphic images or file objects delivered through an HTML e-mail or an internet browser. At just 1 pixel x 1 pixel, they monitor:
If an email recipient has viewed a particular e-mail.
The end user's behavior on a specific web page.
The difference between web beacons and web cookies is that unlike cookies, web bugs cannot be accepted or rejected by the website visitor. Web beacons are not always dangerous or intrusive. They're typically used for:
Measuring the actions of visitors who land on the webpage that contains a clear GIF.
Obtaining high-level web analytics, giving website owners a powerful tool to check user preferences and get valuable data insights.