一般处理程序结合gdi生成简单验证码

using (Bitmap bitmap=new Bitmap(100,40))
{
using (Graphics g=Graphics.FromImage(bitmap))
{
//生成验证码
string s = code();
g.DrawString(s, new Font("黑体", 20), Brushes.Red, 0, 0);
bitmap.Save(context.Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);
}
}

//改变bitmap的颜色循环遍历

for (int j = 0; j < 100; j++)
{
for (int i = 0; i < 40; i++)
{
bitmap.SetPixel(j, i, Color.White);
}
}

//生成随机数的方法

private string code()
{
string s = "";
Random rd = new Random();
for (int i = 0; i < 4; i++)
{
int a = rd.Next(0, 10);
s += a.ToString();
}
return s;
}

前台调用以及javascript

<!DOCTYPE html>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
<title></title>
<script>
window.onload = function () {
document.getElementById("img").onclick = function () {
this.src = 'huatu.ashx';
}
}
</script>
</head>
<body>
<img src="huatu.ashx" alt="验证码" id="img" title="点击更换" style="cursor:pointer" />
</body>
</html>

html页内利用jQuery控制验证码的大小