SEO and the image ALT tags
Search Engine Optimization, or SEO, is extremely important in the design of every page of your website. It is a way for the search engine spiders, or bots, to figure out what your page is really about - based on keyword density, what sites you are linked to, and what 3rd party websites are linking back to you, among several other things. This, in turn, allows people to find your website in the search engine results, when they search for keywords that are on your webpage.
Using Alternate Text in your images is one factor many new designers overlook. Basically, this is a tag you can put with each image, to display a description of what the image is. This can be crucial information, since search engine spiders cannot see the image itself, and many people are either visually impaired and have special browsers that read webpages to them, or have set their browser to "text only" mode, so they don't see any images at all. As a web designer, you probably rely on photographs or other images to enhance the content of the webpage.
To create ALT text for an image, modify your IMG SRC tag to look like this:
<img src="imagefile.jpg" alt="This is my alt text description" title="this is the text that shows when I mouseover the image" />
So, as you can see, image ALT tags can give you an opportunity to punctuate keywords into your content, however you should be careful not to "keyword spam", as this will actually cause you to lose ranking in the search results with many of the major search engines. Keyword density needs to be carefully balanced so that it doesn't go over the top and get penalized for keyword spam.
The algorithms that the search engines use are getting more advanced and intelligent every year, so trying to cheat them is not worth it. Use an accurate description of your image in your ALT tag, or it may make your page sound like complete gibberish to somebody using a screen reader. Your keywords should make up about 8% of your total content at the very most. You want the rest of your content to be readable, relevant, and helpful to human visitors.
If you want to see what your webpage looks like to a search engine spider, and get the keyword density count of any of your webpages, I suggest using the free Spider Simulator Tool at feedthebot.com.