Pixel tracking is a client-side method of recording conversions. A small piece of code, historically a 1x1 transparent image and now often a JavaScript tag or iframe, is placed on the confirmation page. When the user's browser loads that page, the pixel sends a request to the tracking platform, which reads its cookie to identify the click and credits the affiliate.
How it works
- On click, the tracker sets a cookie in the user's browser containing the click or affiliate ID.
- The advertiser places the pixel on the thank-you or order-confirmation page.
- When the page loads, the browser requests the pixel URL, sending the tracker's cookie (if the browser allows it) and any values the advertiser passes, such as order ID and amount.
Because the tracker's domain usually differs from the advertiser's, the cookie is often a third-party cookie, which several major browsers restrict by default.
Example
An illustrative image pixel:
<img src="https://track.example.com/pixel?offer=12&order_id=A-1009&amount=89.90"
width="1" height="1" alt="" style="display:none">
The advertiser's checkout fills in order_id and amount dynamically; the tracker identifies the affiliate from its cookie.
Why it matters
Pixels are quick to install with no backend work, which is why many smaller advertisers start with them. But they depend on the browser: ad blockers, privacy settings, cookie restrictions, and users who close the tab before the page finishes loading all cause missed conversions. Pixels also cannot report events that happen later on the server, such as a lead approval or a first deposit.
That is why many performance programs prefer S2S tracking through postback URLs, sometimes keeping a pixel as a backup. Compare both approaches in what a postback URL is.
Related: S2S tracking, postback URL, Conversions API.