Bitmap source1 = new Bitmap(Server.MapPath("~/kayitlar/resim.jpg"));
        Bitmap source2 = new Bitmap(Server.MapPath("~/kayitlar/maske.png"));
        var target = new Bitmap(source2.Width, source2.Height, PixelFormat.Format32bppArgb);
        var graphics = Graphics.FromImage(target);
        source2.SetResolution(graphics.DpiX, graphics.DpiY);
        graphics.CompositingMode = CompositingMode.SourceOver;  
        graphics.DrawImage(source1, 0, 0);
        graphics.DrawImage(source2, 0, 0);
        target.Save(Server.MapPath("~/kayitlar/sonuc.jpg"), ImageFormat.Png);