Tracking pixels are little 1x1 pixel images that allow you to keep track of how many users visit your website or see your advertisement.
Look, here is a tracking pixel for you to see:
Ooooh! Isn’t she just the cutest little tracking pixel you have ever seen?!
When you open this email and read about tracking pixels, one of the ways that we will know that you did so is that you will ask our server to download our little tracking pixel.
So, when an advertiser wants to know how many users see their ad they use a tracking pixel. What they do is embed a small, transparent PNG in their advertisement that the user can’t see but the advertiser can keep track of.
Each time a new person visits the website where the ad is, that user has to download the advertisement, including the 1x1 pixel transparent PNG. Everytime a user downloads the image, their computer sends a message to the advertiser’s server saying:
“Hey, send that pixel over to this computer at IP Address 18.104.22.168.”
The server says, “Yes, ma’am,” sends the tracking pixel over to that IP Address, and makes a note of the event in its server logs.
At the end of the day (or week, or month), the advertiser looks at their server logs and counts up all the different IP Addresses who requested that tracking pixel; if 10,000 different IP Addresses requested the tracking pixel be sent to them, that means 10,000 people saw the ad.
[Pop Quiz: If the advertiser was paying $10 CPM how much money would they owe to the publisher?]
This is the same technology that allows web analytic services like Google Analytics and Chartbeat to tell how many people visited your site.
Cocktail Party Fact
Now that you know about tracking pixels, you should put them to work! If there is ever a web service that you use that doesn’t provide you with all the analytics you desire, you can employ tracking pixels to get the information you need.
Since a certain crowd-funding platform doesn’t provide users with information about how many people visit their project page (they only tell you how many people give you money!) a certain clever developer we know stuck a small transparent image onto his page and looked at his server logs to determine his project’s conversion rate (the number of people who visited the project page and gave money).