Below is a function that takes two images as parameter with their coordinates and Height Width and stitches both the images together with their respective coordinates and returns a new image.

 public Bitmap StitchImages(Bitmap baseImage, int baseImageWidth, int baseImageHeight, int baseImageXcord, int baseImageYcord, Bitmap sourceImage, int sourceImageW
idth, int sourceImageHeight, int sourceImageXcord, int sourceImageYcord)
        {

            try
            {
                baseImage = new Bitmap(baseImage);
                //Create a new image for Drawing
                var bitmapImage = new System.Drawing.Bitmap(baseImage.Width, baseImage.Height, PixelFormat.Format32bppPArgb);//Creating Image with New dimentions
                var graphic = System.Drawing.Graphics.FromImage(bitmapImage); //Initialising graphic class object with bitmap image

                //Adding Effects to Graphic
                graphic.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
                graphic.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
                graphic.PixelOffsetMode = System.Drawing.Drawing2D.PixelOffsetMode.HighQuality;
                graphic.DrawImage(baseImage, 0, 0); //Draw baseImage with Graphic class
                graphic.DrawImage(sourceImage, sourceImageXcord, sourceImageYcord, sourceImageWidth, sourceImageHeight); //Draw sorceimage over base image on defined coordinates


                var ms = new System.IO.MemoryStream(bitmapImage.Width * bitmapImage.Height);
                bitmapImage.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                System.Drawing.Image img = System.Drawing.Image.FromStream(ms);
                return new Bitmap(img);

            }

            catch (Exception e)
            {
                Response.Write("<script>alert(" + e + ")</script>");
                return null;
            }
        }