// assume that form is bound to $form and file input is named image
// @requires: jQuery, jQuery validate


// an array of valid file types
var whitelist = ['png','jpe?g','gif'];

$form.validate(
	rules : {
		image : {
                accept: whitelist.join('|');
            }
	},
	message : {
		image: {
			accept: "Please upload a valid file type."
		}
	}
);