Upload your image to the template folder, for example:site/templates/email/contact-form/assets/your-logo.png.
You can embed the image directly into the HTML of your email template using the base64_encode() function. Below is an example of how to include the image:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
</head>
<body>
<img src="data:image/png;base64,<?= base64_encode(file_get_contents(__DIR__ . '/assets/your-logo.png')) ?>" alt="Logo">
</body>
</html>
This method will ensure that the image is displayed correctly when the email is received, without needing to rely on external image URLs.