HTML

<img src="" class="VerifiImg" />
<input type="hidden" id="randomNum" />

JavaScript

// 隨機數
		function getRanNum() {
			var str = '';
			for(var i = 0; i < 4; i++) {
				var ranNum = Math.ceil(Math.random() * 9);
				str += ranNum.toString();
			}
			$("#randomNum").val(str);
		}

		getRanNum();
		
//獲取驗證圖片
		function Refresh() {
			var Verificode = $("#randomNum").val();
			console.log(Verificode);
			$('.VerifiImg').attr("src",url?code=" + Verificode);

		}
		Refresh();
		
//點選更換驗證碼
		$('.VerifiImg').click(function() {
			getRanNum();
			Verificode = $("#randomNum").val()
			Refresh();
		})