1. The Alt AttributeThere's really nothing special about the Alt attribute other than it gives you a great opportunity to place another reference to those targeted keywords on your page.
Acceptable Usage of the Alt Attribute for SEO
<img src="searching.jpg" alt="SEO, web programming, search engine optimization, address bar, surfing the web">
<img src="code.jpg" alt="programming, web programming, HTML, CSS, Java, websites">
It looks even worse when the picture fails to load.
You should see either the alt text alone, or the symbol for a broken picture along with the alt text.