title: iTextSharp writer.AddDirectImageSimple throws exception
body: <p>What could be the problem for writer to throw an error, when the code seems correct?  Image also exists.</p>
  
  <pre><code>var img2 = iTextSharp.text.Image.GetInstance("C:\\2.bmp");
  
  writer.AddDirectImageSimple(img2);
  
  at System.ThrowHelper.ThrowKeyNotFoundException()
  at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
  at iTextSharp.text.pdf.PdfWriter.AddDirectImageSimple(Image image, PdfIndirectReference fixedRef)
  at iTextSharp.text.pdf.PdfWriter.AddDirectImageSimple(Image image)
  </code></pre>