Whitey - 11:14 am on Oct 5, 2011 (gmt 0)
but i always thought this alt tag has not that much to do with the ranking
Maybe some folks that are focused on images can chime in with a better answer than me, but i think image search can be very important. Especially as it seems to be your target and call to action.
Still would like to hear if it's part of Panda algo though - again i assume so as it is a potential quality / relevance signal.