2003.09.30 15:16 "[Tiff] Reading thumbnail", by Kai-Uwe Behrmann
By reading TIFF Specification, full-size image is in IFD0 and thumbnail is in IFD1.
So, I was trying to get thumbnail data by calling TIFFSetDirectory(tifr,1) after calling TIFFOpen( ).
libtiff start IFD counting with 0. Please try TIFFSetDirectory(tifr,0).