效果图：
源代码：
<!DOCTYPE html>
<html>
<!-- head -->
<head><title>js验证码</title><script type="text/javascript">/* 定义全局变量用以获取得到的验证码*/
var verification_code = [];
draw(verification_code);
/* 点击更换验证码*/
function code(){draw(verification_code); }
function submit(){var val=document.getElementById("verification").value; /* 数组名.join("。");获取数组内容并按。隔开;例如a[0]='1';a[1]='2';a.join(",)的结果为"1,2"*/var num = verification_code.join("");num = num.toLowerCase();val = val.toLowerCase();if(val==''){alert('请输入验证码！');}else if(val == num){alert('提交成功！');document.getElementById(".input-val").val('');draw(verification_code);}else{alert('验证码错误！请重新输入！');document.getElementById("verification").value='';draw(verification_code);}}
function draw(verification_code) {var canvas_width=document.getElementById('canvas').clientWidth;var canvas_height=document.getElementById('canvas').clientHeight;var canvas = document.getElementById("canvas");//获取到canvas的对象，演员var context = canvas.getContext("2d");//获取到canvas画图的环境，演员表演的舞台canvas.width = canvas_width;canvas.height = canvas_height;var sCode = "A,B,C,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,W,X,Y,Z,1,2,3,4,5,6,7,8,9,0,q,w,e,r,t,y,u,i,o,p,a,s,d,f,g,h,j,k,l,z,x,c,v,b,n,m";var aCode = sCode.split(",");var aLength = aCode.length;//获取到数组的长度for (var i = 0; i <= 3; i++) {var j = Math.floor(Math.random() * aLength);//获取到随机的索引值var deg = Math.random() * 30 * Math.PI / 180;//产生0~30之间的随机弧度var txt = aCode[j];//得到随机的一个内容verification_code[i] = txt;var x = 10 + i * 20;//文字在canvas上的x坐标var y = 20 + Math.random() * 8;//文字在canvas上的y坐标var z = Math.floor(Math.random() * (25-13)+13); /* 字号大小随机在13px-25px之间 */ context.font = "bold " + z+"px Arial";context.translate(x, y);context.rotate(deg);context.fillStyle = randomColor();context.fillText(txt, 0, 0);context.rotate(-deg);context.translate(-x, -y);}for (var i = 0; i <= 5; i++) { //验证码上显示线条context.strokeStyle = randomColor();context.beginPath();context.moveTo(Math.random() * canvas_width, Math.random() * canvas_height);context.lineTo(Math.random() * canvas_width, Math.random() * canvas_height);context.stroke();}for (var i = 0; i <= 30; i++) { //验证码上显示小点context.strokeStyle = randomColor();context.beginPath();var x = Math.random() * canvas_width;var y = Math.random() * canvas_height;context.moveTo(x, y);context.lineTo(x + 1, y + 1);context.stroke();}}
function randomColor() {//得到随机的颜色值var r = Math.floor(Math.random() * 256);var g = Math.floor(Math.random() * 256);var b = Math.floor(Math.random() * 256);return "rgb(" + r + "," + g + "," + b + ")";}</script></head>
<body onload="code()"><input type="text" value="" placeholder="请输入验证码（区分大小写）" style="height:43px; font-size:20px;float:left" id ="verification">
<!--要将canvas转换为块级元素，display:block不然无法对齐--><canvas id="canvas" width="100px" height="43px" onclick="code()" style="border: 3px solid #ccc;display:block;float:left"></canvas><input type="button" onclick="submit()" value="提 交" style="height:48px"></body></html>
参考：https://www.jb51.net/article/151432.htm
