Tagged Images Not Reading

Maybe you know a quick answer to this question or a tutorial I should read:
I'm trying to set up accessibility in a pdf in Acrobat 8. I put three images on a blank page and export them to pdf. I then tag the images in Acrobat 8 and add alt text to their alt text fields. But I ask the file to read itself and it just says its a blank page. (I did not close and reopen the files.) What is wrong with my test? (And is there also a setting for rolling over and seeing the alt text?)