[jQuery] limiting # of elements by attr()

[giannandrea]

Id like to run though all the elements of a particular class/name on a
page and unhide only the first of each that have a particular
attribute.  for example imagine a table with many img tags, and we
want to show only one of each href.

    var id;
    var singleton = function() {if((this != id) && (id = this))
{return true} else {return false}}
     $("img").hide().filter(singleton).show();

but how to have the singleton function check the attribute value for
src= ??