One area where there is a lot of confusion in accessibility is the use of alternate content. There are questions about where it belongs, what form it should take, and whether it is acceptable or not. I’ll be addressing a few of the basics here. We’re going to leave more advanced questions like what to do with multimedia content for a later entry.
Where to supply alternate content
What to put there
Simply put, if the image is meaningless, like a spacer gif or decorative swirl, use an empty alt attribute alt=””. For images that convey information, such as illustrations in a manual, use the text to convey the information rather than describe the colors or size of the image (unless those are informative rather than decorative). For noscript try to ensure that critical information and core functionality are still available to all users. For object tags this can be very difficult, if users are missing an RIA then the best you may be able to do is point them to any other online resources and perhaps a customer support phone number to assist them. In any case always try to include comparable information and functionality.
What is acceptable