Draw border on detect object in image

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C#2.0

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C#

ASP.NET

GDI

GDI+

Hi,
I am developing a web application which are based on image processing. I am not able to fix one issue in my application. I want to draw border on transparent images. i.e for a round transparent image I need to draw border round shaped. Need to detect whole image path and draw border based on that. I used something like

var borderColor = Color.White;

            var newSize = new Size(
                original.Width + borderWidth * 2,
                original.Height + borderWidth * 2);

            var img = new Bitmap(newSize.Width, newSize.Height);
            var g = Graphics.FromImage(img);

            g.Clear(borderColor);
            g.DrawImage(original, new Point(borderWidth, borderWidth));
            g.Dispose();

but this is not working based on transparent image.