How to trigger JavaScript/jQuery on AJAX-enabled ImageField submit?
I agree with DeeZone that .click() should work.

Try putting that code in a $(document).ready();

Drupal ajaxifies it's stuff on document ready so your code might be executing BEFORE the form gets ajaxified by Drupal.

$(document).ready(function() {
  $('#edit-field-image-und-0-upload-button').click(function () {
  alert('hi');
  });
});