How do I create an image pixel for tracking email opens and clicks?
Matthew Whittaker
Co-founder & CTO, Suped
Published 2 May 2025
Updated 19 Aug 2025
9 min read
Email marketing thrives on data, and understanding how recipients interact with your messages is crucial for optimizing campaigns. One of the oldest yet still widely used methods for gathering this intelligence is through the implementation of image pixels, sometimes called tracking pixels or web beacons. These tiny, invisible images, when embedded in your emails, can signal when an email has been opened and, with a slightly different approach, when a link within it has been clicked.
The concept is straightforward: when an email client loads an image, it makes a request to a server. By uniquely identifying each image request, you can log that a specific email was viewed. Similarly, for clicks, rather than tracking an image load, you intercept link clicks and redirect them through your tracking server before sending the user to their final destination. This allows you to record the click event.
While modern email platforms often handle this automatically, understanding the underlying mechanism is valuable for custom implementations, troubleshooting deliverability issues, or when building your own tracking solutions. Creating your own image pixel for tracking requires a combination of server-side logic to log events and front-end HTML to embed the pixel.
How email tracking pixels work
A tracking pixel is essentially a 1x1 pixel, transparent image (often a GIF) embedded within an email's HTML. It's designed to be invisible to the recipient, yet still load from a server when the email is opened. When the email client fetches this tiny image, your server registers the request, logging it as an "open" event. For a deeper dive into how these function, you can explore resources like this email tracking pixels guide. The magic lies in the URL of this image. Each pixel URL is unique to a specific email and recipient, often containing parameters that allow your server to identify precisely who opened the email and when.
This method provides a basic way to gain insights into audience engagement. For example, if you send a promotional email, the tracking pixel tells you if the recipient opened it, giving you a fundamental measure of interest. However, it's important to note that open rates tracked by pixels are not always perfectly accurate, as many email clients, especially mobile ones, cache images or block them by default, which can impact reporting accuracy. You can read more about how this caching affects reporting in our article on how Gmail's image proxy affects email open tracking.
Email open tracking
Open tracking utilizes a hidden 1x1 transparent image embedded in the email. When the email is opened and images are loaded, a request is sent to your server, which records the event. This method provides a basic indicator of recipient engagement.
Mechanism: Image request to a unique URL associated with the email and recipient.
Data collected: Timestamp of open, recipient ID, email ID.
Accuracy notes: Can be affected by image blocking, proxy servers, and pre-fetching by email clients like Gmail which can lead to inflated or delayed reports.
Email click tracking
Click tracking involves rewriting all links in an email to pass through your tracking server first. When a recipient clicks a link, your server logs the click event before redirecting them to the original destination. This offers more detailed behavioral insights.
Mechanism: URL redirection via your tracking server, recording click before forwarding.
Data collected: Timestamp of click, recipient ID, email ID, specific link clicked, original destination URL.
Reliability notes: Generally considered more reliable for direct user engagement than open tracking, but still subject to bot clicks.
Creating an open tracking pixel
To create an image pixel for open tracking, you need two main components: a server-side endpoint and the HTML image tag itself. The server-side endpoint will be a simple script that logs the request and returns a tiny transparent image. This could be a small PHP, Python, Node.js, or any web-enabled script that processes HTTP requests. The key is that it's designed to be lightweight and fast.
The server script should:
Receive: the request with specific query parameters (e.g., email_id, recipient_id).
Log: these parameters to a database or log file, recording the timestamp.
Return: a 1x1 transparent GIF image. This is crucial for the pixel to remain invisible.
Example Server-Side Code (PHP)php
<?php
// PHP example for tracking pixel
header('Content-Type: image/gif');
header('Cache-Control: no-cache, no-store, must-revalidate');
header('Pragma: no-cache');
header('Expires: 0');
// Get parameters from the URL (e.g., ?email_id=123&recipient_id=abc)
$emailId = isset($_GET['email_id']) ? $_GET['email_id'] : 'unknown';
$recipientId = isset($_GET['recipient_id']) ? $_GET['recipient_id'] : 'unknown';
// Log the open event (e.g., to a file, database, or analytics system)
$logMessage = "[" . date('Y-m-d H:i:s') . "] Email ID: " . $emailId . ", Recipient ID: " . $recipientId . " opened.\n";
file_put_contents('email_opens.log', $logMessage, FILE_APPEND);
// Output a 1x1 transparent GIF (binary data)
echo base64_decode('R0lGODlhAQABAJAAAP8AAAAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==');
?>
The HTML for embedding this pixel in your email would then look like this:
Click tracking is slightly different from open tracking because it involves rewriting the links in your email. Instead of linking directly to your target URL, you'll redirect the click through your own server. This allows you to log the click event before the user reaches their final destination. The process also requires a server-side script that acts as a redirector.
Here's how it generally works:
Link Rewriting: Every link in your email (e.g., https://yourproduct.com/pricing) is converted into a tracking link (e.g., https://yourdomain.com/track/click.php?url=encoded_original_url&email_id=12345&recipient_id=abcdef). The url parameter is the original destination URL, typically URL-encoded.
Server-Side Logic: When a user clicks the tracking link, their browser sends a request to your tracking server.
Logging and Redirect: Your server records the email_id, recipient_id, and original_url. Immediately after logging, it issues an HTTP redirect (e.g., a 302 Found) to the original_url.
Example Server-Side Code (PHP)php
<?php
// PHP example for click tracking redirector
// Prevent caching of the redirect
header('Cache-Control: no-cache, no-store, must-revalidate');
header('Pragma: no-cache');
header('Expires: 0');
// Get parameters from the URL
$originalUrl = isset($_GET['url']) ? urldecode($_GET['url']) : null;
$emailId = isset($_GET['email_id']) ? $_GET['email_id'] : 'unknown';
$recipientId = isset($_GET['recipient_id']) ? $_GET['recipient_id'] : 'unknown';
if ($originalUrl) {
// Log the click event
$logMessage = "[" . date('Y-m-d H:i:s') . "] Email ID: " . $emailId . ", Recipient ID: " . $recipientId . " clicked: " . $originalUrl . "\n";
file_put_contents('email_clicks.log', $logMessage, FILE_APPEND);
// Redirect the user to the original URL
header("Location: " . $originalUrl);
exit;
} else {
// Handle cases where original URL is missing
header("HTTP/1.0 400 Bad Request");
echo "Error: Missing URL parameter.";
}
?>
This method ensures that every click passes through your server, providing accurate and detailed analytics. For more insights into how tracking links can impact deliverability, you might find our article on whether HTTP tracking links affect email deliverability insightful.
Considerations and best practices
While image pixels and redirect links are effective for tracking, there are several important considerations to keep in mind to ensure accuracy and maintain good email deliverability. A significant factor is how various email clients handle images and links. For instance, some clients, like Gmail and Outlook, cache images or proxy them through their own servers, which can sometimes lead to inflated open rates or very fast opens, as the pixel might load before the user actually views the email. For detailed information on this, refer to our page on how Gmail's image proxy affects email open tracking.
Furthermore, email tracking pixels can sometimes (but not always) raise red flags with spam filters, depending on their implementation and your sender reputation. While HubSpot, for example, notes that they embed invisible one-pixel images for tracking, it is generally accepted that simply having a pixel doesn't directly cause emails to be marked as spam. However, a poor sender reputation combined with aggressive tracking can contribute to deliverability issues. This is why it is vital to adhere to best practices.
It's also worth considering that different email clients and security settings can affect how tracking pixels behave. Some users might have images blocked by default, or their client might strip out certain HTML elements, impacting your ability to track opens. This also applies to blocklists (or blacklists), which can prevent your emails from reaching the inbox, thus preventing pixels from loading. An in-depth guide to email blocklists can provide more context on these broader deliverability challenges.
Here are some best practices for implementing email tracking pixels and click redirects:
Use a dedicated subdomain: Host your tracking pixels and redirect scripts on a dedicated subdomain (e.g., track.yourdomain.com). This isolates your main domain's reputation from potential tracking-related issues and helps with brand consistency.
HTTPS for tracking URLs: Always use HTTPS for your tracking URLs. This ensures secure communication and is increasingly a requirement for email clients and for maintaining sender trust.
Transparent GIF: Ensure your pixel image is truly a 1x1 transparent GIF. This makes it invisible and minimizes its impact on email loading times.
Fallback content: Provide alternative text (alt="") for the image tag in case images are blocked. Although the pixel is invisible, this is good practice for accessibility.
Caching headers: Set appropriate caching headers for your pixel image to prevent browsers and email clients from caching it excessively, which can skew open rate data.
Monitor deliverability: Regularly monitor your email deliverability and inbox placement rates. If you notice a sudden drop, your tracking setup could be a contributing factor, though it's more likely related to content or sender reputation. You can use a blocklist checker to see if you have been blocklisted.
Accuracy of tracking
Be aware that pixel-based open tracking is not 100% accurate. Factors like image blocking by email clients, proxy servers, and pre-fetching can lead to discrepancies. For more reliable open rate measurement without relying on pixels, explore alternative methods.
Views from the trenches
Best practices
Always use a dedicated subdomain for your tracking pixels and click redirects to insulate your primary domain's reputation.
Implement HTTPS for all tracking URLs to ensure secure data transmission and improve trust with email providers.
Make sure your pixel is genuinely a 1x1 transparent GIF to ensure it is invisible and doesn't affect email rendering.
Set specific caching headers for your tracking pixel to prevent repeated loads from proxies and more accurately reflect unique opens.
Consider implementing robust server-side logging for both open and click events, including IP address and user agent, for deeper analysis and abuse detection.
Regularly audit your tracking infrastructure to ensure it's performing optimally and not introducing latency or errors.
Common pitfalls
Using the main sending domain for tracking pixels can negatively impact your sender reputation if issues arise.
Failing to use HTTPS for tracking URLs can cause security warnings and deter recipients from clicking.
Not properly handling cached images by email clients can lead to inflated or inaccurate open rates.
Implementing overly complex tracking logic that introduces significant latency, affecting user experience.
Ignoring the impact of tracking on email deliverability, potentially leading to increased spam classifications.
Not providing fallback mechanisms or alt text for pixels, which can impact accessibility for some users.
Expert tips
For advanced tracking, combine pixel tracking with other methods like unique link parameters and custom headers.
Look into server-side analytics or log analysis tools to gain more granular insights from your tracking data.
Regularly test your tracking pixels across various email clients and devices to ensure consistent performance.
Be mindful of privacy regulations (like GDPR) when collecting data via tracking pixels and ensure transparency with users.
Consider the trade-offs between self-hosting tracking and using a dedicated email service provider's built-in tracking features.
Analyze not just opens and clicks, but also the time difference between them to identify potential bot activity or pre-fetching.
Marketer view
Marketer from Email Geeks says they were looking for basic open and click tracking functionality that could be integrated into a custom dashboard they were building.
2020-08-25 - Email Geeks
Marketer view
Marketer from Email Geeks says it really depends on what you're trying to track and where, noting that many email service providers (ESPs) or Mail Transfer Agents (MTAs) have built-in tracking. They also suggested exploring tools like Google Tag Manager for this purpose, though they haven't personally used it for email tracking.
2020-08-25 - Email Geeks
Measuring your email engagement
Creating an image pixel for email open tracking and implementing click tracking through redirect links provides valuable insights into how your audience interacts with your campaigns. While the underlying principles are straightforward, successful implementation requires attention to detail, especially concerning server-side logic, HTML embedding, and adherence to deliverability best practices. These methods form the backbone of email analytics, allowing marketers to measure engagement, optimize content, and ultimately drive better results from their email programs.
Understanding the nuances, such as how email clients handle images and the potential impact on deliverability, is essential for accurate reporting and maintaining a strong sender reputation. By carefully designing and monitoring your tracking infrastructure, you can ensure that the data you collect is reliable and actionable, helping you refine your email strategy for maximum impact.
Gmail which can lead to inflated or delayed reports.
Outlook, cache images or proxy them through their own servers, which can sometimes lead to inflated open rates or very fast opens, as the pixel might load before the user actually views the email. For detailed information on this, refer to our page on how Gmail's image proxy affects email open tracking.
HubSpot, for example, notes that they embed invisible one-pixel images for tracking, it is generally accepted that simply having a pixel doesn't directly cause emails to be marked as spam. However, a poor sender reputation combined with aggressive tracking can contribute to deliverability issues. This is why it is vital to adhere to best practices.
