CLEAR PIXEL WEB (beacons)TRACKING
 

clear pixel GIF's (also referred to as "web beacons") to measure page views and email responses. These devices allow us to identify unique visitors to our site and act as a counter for ongoing monitoring of site, email and corresponding future transaction activity related to a specific offer.

Web Beacons (aka clear Pixel GIF's, or "web bugs") are a relatively new tracking technology that, in concert with cookies, can be used for tracking and recording all kinds of behavior across web sites. Because they are generally only 1x1 pixels in size (about the size of a pin point), they are invisible to you. We may use web beacons to monitor page views as a counter within our site.

this is how they do it........ _ Raven