During the website creation process, most people include graphics or photos to draw attention and demonstrate content more attractively. They can also improve search engine optimization in ways that have nothing to do with ALT tags and descriptions. Consider this example:
If you run an adventure travel website and have a page focused on the keyword phrase “African safari camp,” that term may not coincide neatly with a pithy marketing message like “Call Today for 20% Savings!” This call to action may get attention from site visitors, but it does nothing for search engines. However, putting the “Call Today” text in the graphic and using “African Safari Camp” as a heading above it does. Your SEO combines neatly with the message you want to give to consumers.
As you can see, images provide good website real estate for your advertising message even if it does not include targeted keywords. Using the above method ensures that they are accessible to the search engines and that site visitors will still get all the information they need about your special offers.