Accessible Table does not recognize a linked image

Greetings,

I am trying to tag a table that has some images that are linked to various websites. I am able to tag the contents of the table and the links work.

The only problem I have is that the "Alt" text does not display. We have tried to set the Alt numerous times and when you look at the properties, the text shows.. Here is an example of the table

This was originally created with Indesign and expoeted to a PDF. Then the contents were tagged using Acrobat Pro 11.

Any insights would be greatly appreciated.