jQuery.fn.checkboxToggle = function(opt){

   var check = jQuery(this).next()[0].checked == true;
   jQuery(this)
		   .attr({ src: check ? opt.unchecked : opt.checked })
		   .next()[0].checked = !check;
}

jQuery.fn.checkbox = function(opt){
   jQuery(":checkbox", this)

	   // Hide each native checkbox
	   .hide()

	   // Iterate through checkboxes and do all the magical stuff
	   .each(function (){

		   jQuery("<img>")

			   // Set image attributes
			   .attr({src: this.checked ? opt.checked : opt.unchecked, alt: "" })

			   //
			   .click(function() {
				   jQuery(this).checkboxToggle(opt);
			   })

			   // Attach image
			   .insertBefore(this);
	   });
}