What Is the Difference Between a Pixel and a Cookie?

The analysis reveals distinct operational, storage, and control differences between pixels and cookies as web tracking technologies. Pixels—often termed "tracking pixels"—function as transparent images embedded in web content, primarily to collect behavioral data (Haddadi et al., 2010). Cookies, conversely, are small data files stored on the user’s device by a browser, supporting both data storage and user tracking (Soltani et al., 2010).

Key findings:

• Data Collection Mechanism: Pixels transmit data to external servers through HTTP requests each time content loads, enabling remote, continuous user tracking without device storage.
• Persistence and Accessibility: Cookies persist on devices until expiry or deletion, facilitating session continuity and personalization. Pixels lack persistence, operating solely upon content load.
• User Agency: Cookies are subject to increasing regulatory scrutiny (e.g., GDPR), which mandates transparency and opt-out options. Pixels, being invisible and not device-resident, are less directly regulated but can be blocked via content filters.
• Combined Use: Pixels often work alongside cookies; for example, a pixel may trigger the creation or reading of a cookie for advanced tracking purposes.

“Web tracking is achieved through a combination of persistent identifiers (cookies) and stateless identifiers (pixels), each with unique privacy implications.”