Antibots images are needed for avoiding Trojans to make fake registration with out human interaction.In the method given below generate random strings and generate the bitmap of that.This method Should be added as web handler(ashx) in the asp.net project.
public void ProcessRequest(HttpContext context)
{
if(context.Session["antibotimage"] == null)
{
context.Session["antibotimage"] = generateRandomString(4).ToUpper();
}
GenerateImage(context.Session["antibotimage"].ToString(), 100, 20, "Arial").Save(context.Response.OutputStream, ImageFormat.Jpeg);
}
private Bitmap GenerateImage(string text, int width, int height, string fontFamily)
{
Random random = new Random();
// Create a new 32-bit bitmap image.
Bitmap bitmap = new Bitmap(width, height, PixelFormat.Format32bppArgb);
// Create a graphics object for drawing.
Graphics g = Graphics.FromImage(bitmap);
g.SmoothingMode = SmoothingMode.AntiAlias;
Rectangle rect = new Rectangle(0, 0, width, height);
// Fill in the background.
HatchBrush hatchBrush = new HatchBrush(HatchStyle.Wave, Color.LightGray, Color.White);
g.FillRectangle(hatchBrush, rect);
// Set up the text font.
SizeF size;
float fontSize = rect.Height + 1;
Font font;
StringFormat format = new StringFormat();
format.Alignment = StringAlignment.Center;
format.LineAlignment = StringAlignment.Center;
// Adjust the font size until the text fits within the image.
do
{
fontSize--;
font = new Font(fontFamily, fontSize, FontStyle.Bold);
size = g.MeasureString(text, font, new SizeF(width, height), format);
} while (size.Width > rect.Width);
// Create a path using the text and warp it randomly.
GraphicsPath path = new GraphicsPath();
path.AddString(text, font.FontFamily, (int)font.Style, font.Size, rect, format);
float v = 4F;
PointF[] points =
{
new PointF(random.Next(rect.Width) / v, random.Next(rect.Height) / v),
new PointF(rect.Width - random.Next(rect.Width) / v, random.Next(rect.Height) / v),
new PointF(random.Next(rect.Width) / v, rect.Height - random.Next(rect.Height) / v),
new PointF(rect.Width - random.Next(rect.Width) / v, rect.Height - random.Next(rect.Height) / v)
};
Matrix matrix = new Matrix();
matrix.Translate(0F, 0F);
path.Warp(points, rect, matrix, WarpMode.Perspective, 0F);
// Draw the text.
hatchBrush = new HatchBrush(HatchStyle.DashedUpwardDiagonal, Color.DarkGray, Color.Black);
g.FillPath(hatchBrush, path);
// Add some random noise.
int m = Math.Max(rect.Width, rect.Height);
for (int i = 0; i < (int)(rect.Width * rect.Height / 30F); i++)
{
int x = random.Next(rect.Width);
int y = random.Next(rect.Height);
int w = random.Next(m / 50);
int h = random.Next(m / 50);
g.FillEllipse(hatchBrush, x, y, w, h);
}
// Clean up.
font.Dispose();
hatchBrush.Dispose();
g.Dispose();
return bitmap;
}
private string generateRandomString(int size)
{
StringBuilder builder = new StringBuilder();
Random random = new Random();
char ch;
for (int i = 0; i < size; i++)
{
ch = Convert.ToChar(Convert.ToInt32(Math.Floor(26 * random.NextDouble() + 65)));
builder.Append(ch);
}
return builder.ToString();
}
Programmed by
Renju.R,
Software Engineer,
ISOFT, Chennai,India
