code: function(value, element, param) {
  			param = typeof param == "string" ? param.replace(/,/g, '|') : "png|jpe?g|gif";
  			return this.optional(element) || value.match(new RegExp(".(" + param + ")$", "i")); 
  		}
docs: http://docs.jquery.com/Plugins/Validation/Methods/accept