I believe that there was a posted topic long ago that stated "Blind people surf the web everyday" As I discovered Visually Impaired surfers are a huge part of the exchange of money on the web.
We had built a complete shopping cart for a client that sells golf products, and to our surprise we got an email from the organization that caters to blind golfers.
They said that all of the web sites built, very few make it easy to order online. I was asking what made us any different? It was stated that the interpretation system reads off not only text but images as well.
When the golfers made the order, they understood the process because we placed powerful alt tags on each photo of the online golf store.
Point is : ALT Tags can make you money, so don't forget them!