Insert an image in a message from a php form

Let´s see if I can make my point…I have a php form in one of my sites, it is working perfect I receive all the info in my email from the php form, however, I would like to add a top image like a logo to the message I receive in my email, how?

I was thinking in a basic <img src=“http://www.domain.com/header.jpg”"> but I don´t know how to apply it in php…