Can I use plupload to load multiple image files into a single image field
Add this js in your custom js file. 

(function ($) {
  Drupal.behaviors.autoUpload = {
    attach: function (context, settings) {
      $('form', context).delegate('input.form-file', 'change', function() {  
        $(this).next('input[type="submit"]').mousedown();
      }); 
    }
  };
})(jQuery);


It will automatically upload all the images on click of upload button using above Jquery. 

for more information,look at this link. at http://drupal.org/sandbox/clivelinsell/1587560 .