How can I disable third-party cookies for < img > tags?

1. Configuring HTTP Headers

We can prevent the browser from sending cookies to third-party services by setting appropriate HTTP headers. For example, you can use the SameSite attribute to control how cookies are sent. SameSite can be configured as follows:

• Strict: Completely blocks third-party cookies.
• Lax: Allows sending cookies when navigating to the target link (e.g., clicking from another link).
• None: Allows sending cookies in all requests, but the Secure attribute must be set to ensure cookies are only sent over HTTPS connections.

For the <img> tag, if the relevant cookie is not set to SameSite=Strict, the browser may still send the cookie in requests. Therefore, controlling cookie sending typically requires cooperation from the third-party service.

2. Using Content Security Policy (CSP)

Content Security Policy (CSP) is an additional security measure that helps prevent Cross-Site Scripting (XSS) attacks and controls which sources resources can be loaded from. For disabling third-party cookies with the <img> tag, we can use CSP to restrict third-party resource loading or further control their behavior.

For example, by setting the following CSP policy, you can prevent all third-party sites from setting cookies when loading images:

plaintext
Content-Security-Policy: default-src 'self'; img-src 'self'

Here, img-src 'self' specifies that images can only be loaded from the current source, so images are not loaded from third-party servers, thus preventing the reception or sending of third-party cookies.

Example

Suppose you have a website where you do not want any third-party images to include cookies. You can add the following HTTP headers in your server configuration:

plaintext
Set-Cookie: widget_session=abc123; SameSite=Strict; Secure

Additionally, include the CSP in the page header:

html
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; img-src 'self'">

After this setup, any <img> tags not from the current site will not be loaded, thus avoiding the use of third-party cookies.

By using these two strategies, we can effectively control and disable third-party cookies for the <img> tag, enhancing user privacy and website security.