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Cookies, Tags and Pixels: Tracking Customer Engagement

Phil Gross, Assoc. Director, Product Management, Visual IQ

Cookies, Tags and Pixels: Tracking Customer Engagement

One of the frequently asked questions about the “plumbing” that enables the marketing attribution process to function is how individual users can be tracked. How does attribution management software recognize that the same person who saw a Wall Street Journal display ad yesterday also arrived on a website by way of a search click today, and then subsequently purchased?

This is accomplished by stringing together all of the marketing touchpoints to which a user was exposed to create an engagement stack – a chronologically ordered list of all the marketing touchpoints experienced by an individual user. In the previous example, this was a three-touch engagement stack (Wall Street Journal ad yesterday, search click today, conversion today). You can imagine that in many companies’ marketing ecosystems there can be millions of users and their individual engagement stacks.

Tracking users and their engagement stacks is at the core of a modern, algorithmic-fractional attribution methodology. There are several tracking technologies that make this possible. The most common types of tracking technologies are cookies, click redirects, image tags, and tag containers.


Cookies are a simple technology that have been around since the early days of the web. They are pieces of code that web servers use to put information on a user’s browser, and then retrieve that information at a later time for various uses. For example, YouTube sets a cookie on your browser to remember your user name and volume settings so you don’t have to input those every time. Cookies are privacy conscious by design, so that only the server domain that sets a cookie is able to retrieve it.

Ad servers (such as DoubleClick or Atlas) use cookies to set unique IDs so they can identify the same user across multiple touchpoints. When an ad server receives an ad display request from a user who does not have an existing cookie, the ad server assigns a new unique ID (a random alpha-numeric string such as 118D132F9423). On each subsequent request the cookie returns the same unique ID, thus allowing the ad server to know that it is the same user. Because all requests are recorded by the ad server, reports can be created that provide a record of all the touchpoints for each user.

Click Redirects

For media running outside of the ad server, such as paid search, one approach is to apply click redirects within the URL. These briefly send the user through the ad server to be cookied and then shoot them back out to their desired landing page. This happens in a fraction of a second and is barely perceptible by the user. Because that intermediate hop is on the ad server domain, it can log the data needed to record and read the cookie for the unique ID.

Pixel Tags

For media without a click event (such as navigating to a site directly), click redirects cannot be used. In those cases, the solution is to use pixel tags (also known as tags, 1x1 pixels, or web bugs). Pixel tags are typically single pixel, transparent GIF images that are added to a web page. Even though the pixel tag is virtually invisible, it is still served just like any other image you may see online. The trick is that the web page is served from the site’s domain while the image is served from the ad server’s domain. This allows the ad server to read and record the cookie with the unique ID and the extended information it needs to record.

Tag Containers

Finally, sometimes tag containers (also called container tags) must be used. Tag containers hold JavaScript code which contains one or more pixel or click tags. These tag containers can control the information being passed into images, and can decide whether or not to “fire” or show the image tag, which would trigger the ad server to record an impression with the unique ID. A common use for tag containers is to tag users from unpaid impressions such as organic search visits and direct traffic. The attribution process often uses JavaScript to record the referring URL or other information needed to identify and record otherwise untracked conversion paths.

As you can see, there are a host of technologies used to track user engagement stacks for attribution measurement. Once all the touchpoints for a user are recorded by an ad server, attribution software can consume the log files that ad servers provide to do the work necessary to appropriately assign fractional credit to each touchpoint that contributed to a desired outcome.

To learn more about the technologies that enable marketers to monitor and measure each stop on the consumer journey, download our How Cookies, Pixels and IDs Help You Get the Data You Need eBook.

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