Tracking pixel demo
Site A

This page and tracking-pixel-b.glitch.me both include a single-pixel image from tracking-pixel-server.glitch.me, which allows a cookie to be used to track your activity.

Both pages also include an iframe from tracking-pixel-server.glitch.me that shows page visits recorded on pages that include the tracking pixel image.

As you navigate between this site and tracking-pixel-b.glitch.me, the content of the iframe will be updated to show that tracking-pixel-server.glitch.me is tracking your activity on sites that include the tracking pixel.

Refresh this page to update the list of page visits in the iframe.

How it works

1. This pages includes a transparent, 1x1-pixel image from tracking-pixel-server.glitch.me:
   
   <img src="https://tracking-pixel-server.glitch.me/images/tracking-pixel.png">
2. The first time your browser requests the image, the web server at tracking-pixel-server.glitch.me creates a random id to identify your browser. The server also records the date/time and referer URL of the request.
3. In response to the request, the server provides the image, and includes a header: Set-Cookie: id=<id>.
4. When your browser receives the response, it stores the id cookie.
5. The next time you navigate to a page that includes the tracking pixel image from tracking-pixel-server.glitch.me, the header Cookie: user-id=<id> is included in the request for the iframe (if third-party cookies are not blocked).
6. When the tracking-pixel-server.glitch.me web server receives the request, it gets the cookie value, and checks if it already has a record for that id. If so, it adds the details of the current request to the history it has stored. Otherwise it starts a new entry for the id.
7. The iframe content provided in the response is updated, to display the browsing activity that tracking-pixel-server.glitch.me has recorded.