GDI+画曲线外型的变形文字（可用于图形验证码）

先看效果：

关键代码：

        private void DrawWords(Graphics graphics, int width, int height, string phrase)
        {
            graphics.FillRectangle(Brushes.White, 0, 0, width, height);


            using (var gp = new GraphicsPath())
            {
                gp.AddString(phrase,new FontFamily("Arial"), (int)FontStyle.Bold, 48f, new Point(0, 0), StringFormat.GenericDefault);


                using (var gpp = GraphicsPathDeform(gp, width, height))
                {
                    var bounds = gpp.GetBounds();
                    var matrix = new Matrix();
                    var x = (width - bounds.Width) / 2 - bounds.Left;
                    var y = (height - bounds.Height) / 2 - bounds.Top;
                    matrix.Translate(x, y);
                    gpp.Transform(matrix);
                    graphics.FillPath(Brushes.Black, gpp);
                }
            }
            graphics.Flush();
        }


        private GraphicsPath GraphicsPathDeform(GraphicsPath path, int width, int height)
        {
            var WarpFactor = 3;
            var xAmp = WarpFactor * width / 100d;
            var yAmp = WarpFactor * height / 50d;
            var xFreq = 2d * Math.PI / width;
            var yFreq = 2d * Math.PI / height;
            Random rng = new Random();
            var deformed = new PointF[path.PathPoints.Length];
            var xSeed = rng.NextDouble() * 2 * Math.PI;
            var ySeed = rng.NextDouble() * 2 * Math.PI;
            var i = 0;
            foreach (var original in path.PathPoints)
            {
                var val = xFreq * original.X + yFreq * original.Y;
                var xOffset = (int)(xAmp * Math.Sin(val + xSeed));
                var yOffset = (int)(yAmp * Math.Sin(val + ySeed));
                deformed[i++] = new PointF(original.X + xOffset,original.Y + yOffset);
            }


            return new GraphicsPath(deformed, path.PathTypes);

        }

测试：

        private void button2_Click(object sender, EventArgs e)
        {
            Bitmap bmp = new Bitmap(600, 600);
            Graphics g = Graphics.FromImage(bmp);
            g.CompositingQuality = CompositingQuality.HighQuality;
            g.InterpolationMode = InterpolationMode.HighQualityBicubic;
            g.TextRenderingHint = System.Drawing.Text.TextRenderingHint.AntiAlias;

            DrawWords(g, 500, 100, "Guangdong, China");
            pictureBox1.Image = bmp;
            g.Dispose();
        }

当然，如果你认为上面的还不够验证要求，还可以加上背景杂色、背景图片或者不规则的线条、曲线等，也可以先将上面的文字进行旋转等变形后，再做上述处理，但有一个大原则：要方便人眼识别，而程序无法识别或很难识别。这里就不再详述。