It's possible to insert images into your Dynamics CRM email templates. The trick is to make sure the content is accessible via public access on the web somewhere.
Create the html for the image in a tool such as Office Word or Visual Studio. Render the html in the browser and then select it. Copy to the clip board and then paste into the template.
If you simply put the html syntax in the email, it is what the user will see. Make sure you copy it from a render browser view.
This way you can insert you own company logo, etc in your email templates.