Tracking pixel
A tracking pixel is a tiny, invisible image embedded in a page or email whose load request signals to the hosting server that the content was opened, along with the viewer’s IP and client details.
Analytics and the web
The mechanism is simple: a 1x1 transparent image tag points at a URL unique to the recipient or session. Loading the page or email triggers an HTTP request for that image, and the mere act of fetching it — not any interaction with visible content — tells the server the content was viewed, when, from what IP, and with what client software. No click or explicit action is required.
On the web, pixels are a common cross-site tracking mechanism, often paired with third-party cookies to build advertising profiles. In email, they are the standard method behind "open tracking": read receipts the recipient never explicitly granted. Because loading remote images can be disabled or blocked, pixel-based tracking is inherently unreliable — but it is also silent, which is what makes it a privacy concern independent of its accuracy.