code: func (f *Fpdf) RegisterImage(fileStr, tp string) (info *ImageInfoType) {
  	options := ImageOptions{
  		ReadDpi:   false,
  		ImageType: tp,
  	}
  	return f.RegisterImageOptions(fileStr, options)
  }
docs: // RegisterImage registers an image, adding it to the PDF file but not adding
  // it to the page. Use Image() with the same filename to add the image to the
  // page. Note that Image() calls this function, so this function is only
  // necessary if you need information about the image before placing it.
  //
  // This function is now deprecated in favor of RegisterImageOptions.
  // See Image() for restrictions on the image and the "tp" parameters.