In developing web sites I try to make them as user friendly and as search engine friendly as I can. Here is a tip to increase both search engine friendliness and user friendliness. Most web sites are designed with images for the header which will load first. Search engines do not recognize images and the alt atribute has a low priority in ranking.
You want a nice image header and a friendly site, so here is what to do?
Place the header in a <div> and load the image as a background image, i.e.
<div style="background-image: url('my_nice_header.jpg'); height:150px; width:760px;"> </div>
(Replace height and width with the height and width of you image. If you use tables the div can be put in a table cell.)
You have now accomplished three things.
1. Your page content will load faster because background images load last.
2. The search engine reads your more important text content first.
3. You can write over the image. I often put the site name in <h1> tags so that this is the first thing that the search engine reads.
<div style="background-image: url('my_nice_header.jpg'); height:150px; width:760px;">
<h1>www.my_domain_name.com (or other text)</h1>