c# 生成验证码图片

   /// <summary>
        /// 生成验证码图片
        /// </summary>
        /// <returns></returns>
        public byte[] getverifycode()
        {
            int codew = 80;
            int codeh = 40;
            int fontsize = 18;
            string chkcode = string.empty;
            //颜色列表，用于验证码、噪线、噪点 
            color[] color = { color.black, color.red, color.blue, color.green, color.orange, color.brown, color.brown, color.darkblue };
            //字体列表，用于验证码 
            string[] font = { "times new roman" };
            //验证码的字符集，去掉了一些容易混淆的字符 
            char[] character = { '2', '3', '4', '5', '6', '8', '9', 'a', 'b', 'd', 'e', 'f', 'h', 'k', 'm', 'n', 'r', 'x', 'y', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'j', 'k', 'l', 'm', 'n', 'p', 'r', 's', 't', 'w', 'x', 'y' };
            random rnd = new random();
            //生成验证码字符串 
            for (int i = 0; i < 4; i++)
            {
                chkcode += character[rnd.next(character.length)];
            }

            //创建画布
            bitmap bmp = new bitmap(codew, codeh);
            graphics g = graphics.fromimage(bmp);
            g.clear(color.white);
            //画噪线 
            for (int i = 0; i < 1; i++)
            {
                int x1 = rnd.next(codew);
                int y1 = rnd.next(codeh);
                int x2 = rnd.next(codew);
                int y2 = rnd.next(codeh);
                color clr = color[rnd.next(color.length)];
                g.drawline(new pen(clr), x1, y1, x2, y2);
            }
            //画验证码字符串 
            for (int i = 0; i < chkcode.length; i++)
            {
                string fnt = font[rnd.next(font.length)];
                font ft = new font(fnt, fontsize);
                color clr = color[rnd.next(color.length)];
                g.drawstring(chkcode[i].tostring(), ft, new solidbrush(clr), (float)i * 18, (float)0);
            }
            //将验证码图片写入内存流，并将其以 "image/png" 格式输出 
            memorystream ms = new memorystream();
            try
            {
                bmp.save(ms, imageformat.png);
                return ms.toarray();
            }
            catch (exception)
            {
                return null;
            }
            finally
            {
                g.dispose();
                bmp.dispose();
            }
        }