/**包装**/
var xh_digital_code = function(option) {
    this.el = option.el;
    var self = this;
    var click_code = '';

    var canvas_id = "xh_canvas_" + xh_randomWord(false, 30);// 生成随机id
    $(self.el).html('<canvas class="xh_canvas" id="' + canvas_id + '"></canvas>');

    var code = xh_drawPic(canvas_id);

    $('body').on('click', self.el, function() {
        click_code = xh_drawPic(canvas_id);
        self.code = click_code;
        return;
    });
    
    self.code = code;
}

/**绘制验证码图片**/
function xh_drawPic(canvasid) {
    var canvas = document.getElementById(canvasid);
    var width = canvas.width;
    var height = canvas.height;
    //获取该canvas的2D绘图环境 
    var ctx = canvas.getContext('2d');
    ctx.textBaseline = 'bottom';
    /**绘制背景色**/
    ctx.fillStyle = xh_randomColor(180, 240);
    //颜色若太深可能导致看不清
    ctx.fillRect(0, 0, width, height);
    /**绘制文字**/
    var str = 'ABCEFGHJKLMNPQRSTWXY123456789abcefghjklmnpqrstwxy';
    var code = "";
    //生成四个验证码
    for (var i = 1; i <= 4; i++) {
        var txt = str[xh_randomNum(0, str.length)];
        code = code + txt;
        ctx.fillStyle = xh_randomColor(50, 160);
        //随机生成字体颜色
        ctx.font = xh_randomNum(90, 110) + 'px SimHei';
        //随机生成字体大小
        var x = 10 + i * 50;
        var y = xh_randomNum(100, 135);
        var deg = xh_randomNum(-30, 30);
        //修改坐标原点和旋转角度
        ctx.translate(x, y);
        ctx.rotate(deg * Math.PI / 180);
        ctx.fillText(txt, 0, 0);
        //恢复坐标原点和旋转角度
        ctx.rotate(-deg * Math.PI / 180);
        ctx.translate(-x, -y);
    }

    /**绘制干扰线**/
    for (var i = 0; i < 3; i++) {
        ctx.strokeStyle = xh_randomColor(40, 180);
        ctx.beginPath();
        ctx.moveTo(xh_randomNum(0, width / 2), xh_randomNum(0, height / 2));
        ctx.lineTo(xh_randomNum(0, width / 2), xh_randomNum(0, height));
        ctx.stroke();
    }
    /**绘制干扰点**/
    for (var i = 0; i < 50; i++) {
        ctx.fillStyle = xh_randomColor(255);
        ctx.beginPath();
        ctx.arc(xh_randomNum(0, width), xh_randomNum(0, height), 1, 0, 2 * Math.PI);
        ctx.fill();
    }
    return code;
}



/**生成一个随机数**/
function xh_randomNum(min, max) {
    return Math.floor(Math.random() * (max - min) + min);
}

/**生成一个随机色**/
function xh_randomColor(min, max) {
    var r = xh_randomNum(min, max);
    var g = xh_randomNum(min, max);
    var b = xh_randomNum(min, max);
    return "rgb(" + r + "," + g + "," + b + ")";
}

/**生成一个随机码**/
function xh_randomWord(randomFlag, min, max) {
    var str = "",
        range = min,
        arr = ['0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'];

    // 随机产生
    if (randomFlag) {
        range = Math.round(Math.random() * (max - min)) + min;
    }
    for (var i = 0; i < range; i++) {
        pos = Math.round(Math.random() * (arr.length - 1));
        str += arr[pos];
    }
    return str;
}

<!--- 引用 --->
<span class="identify-code"></span>
<button class="xh-btn xh-btn-success" id="get_code">获取验证码</button>

<script type="text/javascript">
  var c = new xh_digital_code({
        el: '.identify-code' // .class名 #id名
    });

    $('#get_code').click(function(){
     // 这个是我写的一个弹出信息的插件，不用理会，c.code就可以获取验证码里面的信息
        $(this).xh_prompt('success', '当前验证码为：'+c.code, 1000);
    });
</script>