Saving StrokeCollection from InkCanvas Result in Unsupported format

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WPF

C#3.5

C#5.0

I am saving the StrokeCollection From InkCanvas was Result in Unsupported format. following is the code i am using:

signatureOutStream = new FileStream(newSignImageDirectory + "\\newSign.jpg", FileMode.Create);
    _Signature.Save(signatureOutStream);// here _Signature is the stroke collection
    _Signature.Clear();
    signatureOutStream.Close();
    signatureOutStream.Dispose();

A file is generating But is not able to open. What i am doing wrong?