You can add an image to either an automated or smart Email Notification Response Rule by using HTML and including a img tag in the email body that links to the image that is required.
1. Please make sure that your Enforce is configured for sending emails over your mail server.
SMTP configuration for Enforce
2. Create a response Rule with the "Send Email Notification" action type.
Configuring the Send Email Notification action
Add an HTML img tag to the Body field.
3. Make sure that the Response Rule is used in your policy.