I have a jQuery selector with following syntax:
$(\'input[type=image]\').not(\'.xyzClass\').click(function{ //some functionality });
So
to do an "OR" use a comma:
$('input[type=image]') .not(".xyzClass,[onclick*='someSpecificFunctionality()']") .click(...);
I'm not sure how you're defining the onclick though: is it in your HTML or is added programmatically?