I'm not quite sure if this is off topic... Please explain to me why it is.

As for the alt-attribute: browsers for the visually impaired display (through text, braille or speech) whatever is in the alt-attribute. They should not and fortunately do not say a thing when alt is set but empty. If it's not set at all, some do nothing, some display the picture's filename.
Correct CSS would indeed be a better solution.

This is what links displays:

   clearpixel
   (concentrate on your petition)                      clearpixelJoe
   clearpixel ____________________ [ searchbutton ]        perlmonks
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Alt should provide alternative text for images that need it, or no text for images that are just for layout or decoration.

2;0 juerd@ouranos:~$ perl -e'undef christmas'
Segmentation fault
2;139 juerd@ouranos:~$
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