jQuery canvas draws picture verification code example

.identify-code{
    position: absolute;
    right: 6px;
    top: 50%;
    width: 118px;
    height: 40px;
    margin: -21px 0 0 0;
}

<span id="code" class="identify-code">
  <canvas class="show-captcha" id="canvas" style="width: 100%; height: 100%;"></canvas>
</span>

/**Draw the verification code image**/
function drawPic() {
    var canvas = document.getElementById("canvas");
    var width = canvas.width;
    var height = canvas.height;
    //Get the 2D drawing environment of the canvas var ctx = canvas.getContext('2d'); 
    ctx.textBaseline = 'bottom';
    /**Draw the background color**/
    ctx.fillStyle = randomColor(180, 240);
    //If the color is too dark, it may not be clear ctx.fillRect(0,0,width,height);
    /**Draw text**/
    var str ='ABCEFGHJKLMNPQRSTWXY123456789abcefghjklmnpqrstwxy';
    var code="";
    //Generate four verification codes for(var i = 1;i <= 4; i++) {
        var txt = str[randomNum(0,str.length)];
        code=code+txt;
        ctx.fillStyle = randomColor(50,160);
        //Randomly generate font color ctx.font = randomNum(90,110) +'px SimHei';
        // Randomly generate font size var x = 10 + i * 50;
        var y = randomNum(100, 135);
        var deg = randomNum(-30, 30);
        //Modify the coordinate origin and rotation angle ctx.translate(x, y); 
        ctx.rotate(deg * Math.PI /180); 
        ctx.fillText(txt,0,0);
        //Restore the coordinate origin and rotation angle ctx.rotate(-deg * Math.PI /180);
        ctx.translate(-x, -y);
    }
        
    /**Draw interference line**/
    for(var i=0;i<3;i++) {
        ctx.strokeStyle = randomColor(40, 180);
        ctx.beginPath();
        ctx.moveTo(randomNum(0,width/2), randomNum(0,height/2));
        ctx.lineTo(randomNum(0,width/2), randomNum(0,height));
        ctx.stroke();
    }
    /**Draw interference points**/
    for(var i=0;i <50;i++) {
        ctx.fillStyle = randomColor(255);
        ctx.beginPath();
        ctx.arc(randomNum(0, width), randomNum(0, height),1,0,2* Math.PI);
        ctx.fill();
    }
    return code;
}
/**Generate a random number**/
function randomNum(min, max) {
    return Math.floor(Math.random() * (max - min) + min);
}
/**Generate a random color**/
function randomColor(min, max) {
    var r = randomNum(min, max);
    var g = randomNum(min, max);
    var b = randomNum(min, max);
    return "rgb(" + r + "," + g + "," + b + ")";
}

$("#code").unbind('click').click(function(e){
    e.preventDefault();
    createCode();
});
//Generate verification code function createCode(){
  VerificationCodeErrCount = 0;
  randomCode = drawPic();
  return randomCode;
}