It's easy to get busy and rush through a web template if you're a small business do it yourself-er. And, especially if your site is image intensive, you may fail to key the alt information into each image. If you miss this key set of information, you're missing an important way for search engines to point interested customers to your page.
Search engines run through all the text on your site. An image with no text will be ignored. An image with accurate alt text will not only be friendly to customers who are blind or provide information when pictures don't load properly, but will be read by search engines, the same as any other text. That alt text will then be used by the Search Engine to bring you the customers.
In a way, the alt text is even more important than that image. Don't miss it.