Used in conjunction with an ad server, pixel tags can help provide information on which campaign ads are most effective at driving back-end actions for our clients. Tag critical pages on an advertiser's Web site with 1x1 transparent GIFs, and you give your ad server the opportunity to check to see if a purchaser was referred by your ad campaign. This is accomplished by reading the cookie that was set when the purchaser viewed an ad. Most marketers using pixel tags use them for this reason. It's a fairly innocent practice.
Most marketers use pixel tags to help determine which ads are performing best in a given campaign.
Tracking the best-performing ads helps us to optimize campaigns and determine where our customers are. Very few marketers wish to use this technique to build profiles, collect personally identifiable information, or violate the privacy of Web users in any way. Yet we haven't taken adequate steps to educate the Web community about our intentions here. And we also haven't done enough to ensure that pixel tagging isn't abused. This recent post at Slashdot is indicative of a new backlash against the practice.