QUOTE(Why @ Sep 27 2007, 08:31 PM)
Is it authorized to put text in an image and make a link on it?
Of course. It's used by many, many sites for their site navigation without any problems. Naturally, without alt attribute text these graphical links won't be particularly accessible to the handicapped.
Trying to hide them is liable to bring down many more problems than simply leaving them, especially when your reason is something as pointless as word density.
To be honest, I agree...