It is an SEO tactic that if you want only a header image instead of displaying the title and tagline, you can use "alt" text instead and Google will count it as <h1>.
Code:
<h1>
<a href="http://example.com">
<img src="header.png" alt="Your Site Name" />
</a>
</h1>
How would I implement all the parts (the h1, the link, the image, and the alternate text) in an SEO friendly way in Atahualpa?