Re: fear of "invisible metadata"

Sander Tekelenburg wrote:

 >> <li><a><img title="a butterfly" alt="an image of a butterfly"></a></li>
 >>
 >> That seems sort of pointlessly repetitive to me.
 >
 > Indeed. The text "an image of a butterfly" is complementary, not an
 > alternative. It can make sense for a title attribute but is useless as ALT
 > text.

I am interested in this assertion.  Suppose, instead, the ALT text
read "Papilio xuthus : photographed resting on leaf of Phelloderldron amurensis;
image taken using Zuiko macro lens at 4cm on Olympus OM4-Ti, f/16, 0,5 seconds,
ISO 100 (ring flash); photograph taken 05:17 on Monday 18-Jun-2006, Kuril Island".
Would that also be (in your opinion) "useless as ALT text", and if so, can you
suggest what suitable ALT text might be ?

Philip Taylor