A lot of images format use Exif to store there metadata. As Exif is
based on the TIFF structure, the TIFF decoder can, without modification
be able to decode the metadata. We only need a new API to explicitly
mention that we only need the metadata.
Support for JPEGs embedded in TIFF images was introduced with TIFF 6.0.
However, this implementation had major issues. It was so problematic
that they decided to reimplement it from scratch in 1995, three years
later. The two incarnations are obviously incompatible.
For more details see:
https://www.awaresystems.be/imaging/tiff/specification/TIFFTechNote2.txt
