How Google handles alt text in H1 tags

It’s well accepted amongst SEOs that alt text in images doesn’t carry as much weight as plain text. However if a website’s CMS automatically uses images as headings to preserve a design, is there any ROI in SEO for the associated costs of implementing sIFR or image replacement techniques?

I ran a quick test in order to test this, and an inference taken from page 16 of Google’s SEO Starter Guide:

“the alt text for that image will be treated similarly to the anchor text of a text link”

The inference here is that alt text in images does not carry as much ranking weight as plain textual content. As mentioned above, this is a generally accepted principle, but I wanted to know if this applied equally to heading tags as everything else.

I linked to 2 almost identical pages, with the heading code differing as follows:

Text version (8lks5c3z.htm): <h1>7i1bn504</h1>
Image version (04×7oszi.htm): <h1><img src=”04×7oszi.jpg” alt=”7i1bn504″ /></h1>

The page with the image-based H1 tag was linked to above text-based H1 to adjust for any bias in HTML order.

As expected, the results showed a clear bias towards the textual version. Google indexed both pages and putting the image-based version in the supplemental results. Yahoo, Ask and Lycos only indexed the textual version (and Bing did not index either version). The images below outline the results: