Do you consider your images when you are working on SEO? Image size and alternate text are two items that you can control and they can both impact your ranks.
The size of your image can have a significant impact on the speed of the page you are trying to get ranked. Too many people put in images that are too large and slow down the process of getting your graphic on the screen of the site visitor. This speed is a key element in the determining of your ranks. Slow pages are not favored by the search engines.