Try KW's advice
Go into the category and head down to the "Custom Fields" section... in there you'll see an option named "Automatically Parse Links In Text" and make sure it is turned on.
The 'gotcha' is that the flag works when images are uploaded or edited but not when they are displayed. That means if you have any existing images with a link in the text that was uploaded before the flag was turned on then they won't be parsed unless the image is edited.
Then try rebuilding pics to see if that update the existing photos so the hyperlink works properly.