==== Exiftool ====
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 
      * <code - .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;
            },
        },
    },
);
</code> 
  * Examples
    * Add Picasa People tags as Keywords ((Check Tools>Options>Name Tags>Store name tags in photo in Picasa to ensure recognized people are written in JPG files (as 'XMP:RegionName'-tag))): <code>exiftool "-Keywords+<RegionName" DIR</code>
    * Add 4 first characters of filename as Keyword (assuming the 4 first characters are the year in which the picture was taken): <code>exiftool "-Keywords+<${filename;$_=substr($_,0,4);s/\..*?$//}" DIR</code>
    * Remove duplicate Keywords: ((UniqueKeywords is defined in .ExifTool_config))<code>exiftool "-Keywords<UniqueKeywords" DIR</code> 
  * Add ''-v0'' (verbose) as parameter to see processed file