Title: Make CAPTCHA images with overlapping characters in C#
The following MakeCaptchaImage2 method creates a Bitmap containing a CAPTCHA image.
private Random Rand = new Random();
// Draw the words with letters overlapping each other.
private Bitmap MakeCaptchaImage2(string txt,
int wid, int hgt, Font the_font, Brush the_brush)
Bitmap bm = new Bitmap(wid, hgt);
using (Graphics gr = Graphics.FromImage(bm))
gr.TextRenderingHint = TextRenderingHint.AntiAliasGridFit;
int x = 0;
foreach (char ch in txt.ToCharArray())
SizeF ch_size = gr.MeasureString(ch.ToString(), the_font);
int y = (int)(Rand.NextDouble() * (hgt - ch_size.Height));
gr.DrawString(ch.ToString(), the_font, the_brush, x, y);
x += (int)(ch_size.Width * 0.35);
The method creates a Bitmap of the desired size. For each character, it measures the character as it will be drawn, picks a random Y coordinate for the character, and draws it. The code then increments the next character's X position by 0.35 times the character's width so the two characters will overlap horizontally.
Download the example to experiment with it and to see additional details.