Here i have explained how to create Captcha Image with Refresh Button in Asp.Net

Step 1) Add HTML:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
<title>Captcha Image with Refresh Button</title>
<script type="text/javascript">
function RefreshCaptcha() {
var img = document.getElementById("imgCaptcha");
img.src = "Handler.ashx?query=" + Math.random();
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<img src="Handler.ashx" id="imgCaptcha" />
<a href="#" onclick="javascript:RefreshCaptcha();">Refresh</a>
</div>
</form>
</body>
</html>

Step 2) Generic Handler Page

Create a generic handler page by name of "Handler.ashx" then put following code.

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Web;

public class Handler : IHttpHandler {
    
public void ProcessRequest (HttpContext context) {
using (Bitmap b = new Bitmap(150, 40, PixelFormat.Format32bppArgb))
{
using (Graphics g = Graphics.FromImage(b))
{
Rectangle rect = new Rectangle(0, 0, 149, 39);
g.FillRectangle(Brushes.White, rect);

// Create string to draw.
Random r = new Random();
int startIndex = r.Next(1, 5);
int length = r.Next(5, 10);
String drawString = Guid.NewGuid().ToString().Replace("-", "0").Substring(startIndex, length);

// Create font and brush.
Font drawFont = new Font("Arial", 16, FontStyle.Italic | FontStyle.Strikeout);
using (SolidBrush drawBrush = new SolidBrush(Color.Black))
{
// Create point for upper-left corner of drawing.
PointF drawPoint = new PointF(15, 10);

// Draw string to screen.
g.DrawRectangle(new Pen(Color.Red, 0), rect);
g.DrawString(drawString, drawFont, drawBrush, drawPoint);
}
b.Save(context.Response.OutputStream, ImageFormat.Jpeg);
context.Response.ContentType = "image/jpeg";
context.Response.End();
}
}
}
 
public bool IsReusable {
get {
return false;
}
}

}

Screenshot

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