Image keyword placement is just one more ingredient to an all around good SEO program.  Each image on your site can and will be indexed by Google.  When you type in a search in Google and click on the "images" area it shows images that relate to your search.  This is another viable way of bringing targeted traffice to your site.

Each image should only contain keywords that are related to the image and associated with the area of the site it is located in.  The concept of placing keywords in images is a commonly overlooked piece of the SEO pie that should not be left out. 

Here at 480SEO we have extensive knowledge of the art of keyword placement.  We target those keywords on the images from your site to add solid traffic from Google's image search.