求Asp.Net验证码图片代码

如题，还包括输入后的验证

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C# code:

/// <summary>
/// 获取随机字符
/// </summary>
/// <param name="count">个数</param>
/// <returns></returns>
private string GetRanStr(int count)
{
string str = "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,0,1,2,3,4,5,6,7,8,9,10";
string[] strArr = str.Split(',');
//随机字符
string validate = "";
Random ran = new Random();
for (int i = 0; i < count; i++)
{
int t = ran.Next(62);
validate += strArr[t];
}
//存储到cookie
Response.Cookies.Add(new HttpCookie("validate", validate));
return validate;
}

/// <summary>
/// 创建验证图片
/// </summary>
private void CreateImage(string validate)
{
if (validate != null || validate.Trim() != string.Empty)
{
Bitmap theBit = new Bitmap((int)Math.Ceiling((validate.Length * 13.5)), 23);
Graphics gra = Graphics.fromImage(theBit);
try
{
Random ran = new Random();
gra.Clear(Color.White);
//画图片的背景噪音线