On page optimization broadly covers everything that you have control over on your webpages, thats every componant that you can see such as:
navigation text (content) images Rich Media Flash (tough to get right, but it needs considered) Links (internal AND external)
The other thing that it covers are the items that you CANT see on your site, thats all code that the browser and therefore the search engine spiders have to contend with. There are multiple reasons why all these elements are important, for instance overall page size (google favours concise pages) and directly related to that is overall pageload time. While data on this is fairly sketchy (perhaps Rand @ seoMOZ can shed some light?) it stands to reason that if all other elements strength wise between page A and page B are the same, well google will likely prefer the quicker loading as it would reduce the effective bounce rate.
There are also a lot of "hidden" items that form the cornerstone of SEO:
Meta Titles Meta Descriptions Meta Keywords (*Yahoo only)
So, lets look at all of these elements individually:
Images
Images are important for SEO for a number of reasons, direct and indirect.
Direct: make totally sure that you use a REAL image alt tag, keyword stuffing is not acceptable anymore - the alt text should be a concise description of the image that you are portraying, for instance if you set your image alt text to: "blue widgets, widgets, blue, widgets in blue, blue colored widgets" that would have zero positive value at all. If it were more like "Image of Blue Widget




