In order to embed HTML, you actually need to copy the rendered HTML from either an existing web page or WYSIWYG HTML editor and then paste it into Gmail.

How to Embed a Picture in Gmail. Inline images add context to your email messages. When appropriate, an embedded image can help brand your company and instill confidence in your customers.

Thanks to some handy tricks in the Google Labs bag you can easily add an HTML signature complete with images and save it for future use without plug- ...

Use HTML signatures in Gmail There have almost certainly been times when either you, or someone you know has asked the question: "How do I use my HTML signature in Gmail?".

A Gmail Labs feature adds the capability of embedding images into your outgoing mail--great for those times when mere words won't do.