code: func (f *Fpdf) RegisterImageReader(imgName, tp string, r io.Reader) (info *ImageInfoType) {
  	options := ImageOptions{
  		ReadDpi:   false,
  		ImageType: tp,
  	}
  	return f.RegisterImageOptionsReader(imgName, options, r)
  }
docs: // RegisterImageReader registers an image, reading it from Reader r, adding it
  // to the PDF file but not adding it to the page.
  //
  // This function is now deprecated in favor of RegisterImageOptionsReader