System.Drawing.Bitmap img = new System.Drawing.Bitmap(300,200);
Graphics g = System.Drawing.Graphics.FromImage(img);
SolidBrush b = new SolidBrush(Color.White);
System.Drawing.Rectangle Ra = new Rectangle(new Point(0,0),new Size(200,200));
g.DrawString(System.DateTime.Now.ToString(),new Font("宋体",20),b,Ra,StringFormat.GenericTypographic);
img.Save(Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);