http://www.sno.phy.queensu.ca/~phil/exiftool/

• Installation
  • Install by renaming "exiftool(-k).exe" to "exiftool.exe" and saving it in c:\Program Files (x86)\exiftool.
  • Add c:\Program Files (x86)\exiftool to %PATH%
  • Create .ExifTool_config in

    • .ExifTool_config

      %Image::ExifTool::UserDefined = (
          'Image::ExifTool::Composite' => {
              UniqueKeywords => {
                  Require => 'Keywords',
                  ValueConv => q{
                      my @list = ref $val eq 'ARRAY' ? @$val : $val;
                      my ($item, %found, @rtn);
                      foreach $item (@list) {
                          $item =~ s/^\s+//;   # remove leading white space
                          push @rtn, $item unless $found{$item};
                          $found{$item} = 1;
                      }
                      return \@rtn;
                  },
              },
          },
      );

• Examples
  • Add Picasa People tags as Keywords ¹⁾): exiftool "-Keywords+<RegionName" DIR
  • Remove duplicate Keywords: exiftool "-Keywords<UniqueKeywords" DIR ((Note: UniqueKeywords is defined in .ExifTool_config)