Use ExifTool instead of Exiv2 to read photo metadata and extract thumbnails.
The default is to use Exiv2, relying on ExifTool only when Exiv2 does not support
the file format being read.
Exiv2 is fast, accurate, and almost always reliable, but it crashes when extracting
metadata from a small number of files, such as DNG files produced by Leica M8
cameras.