Thanks for your reply. I did manage to write in the segment, by creating a new record with store_record and writing directly the record value in the segment buffer

use strict; use warnings;
use Image::MetaData::JPEG;
use Image::MetaData::JPEG::Record;
use Image::MetaData::JPEG::data::Tables
    qw(:JPEGgrammar :Endianness :RecordTypes);

#read the image filname from the command line arguments
my $file = new Image::MetaData::JPEG($ARGV[0], 1);

#create the APP2 segment, do not parse it as it is empty
my $buffer;  #the buffer that will contains the data to write in the s
+egment
my $segref = new Image::MetaData::JPEG::Segment('APP2', \$buffer, 'NOP
+ARSE');


my $MP_FORMAT_IDENTIFIER = chr(hex '4D').chr(hex '50').chr(hex '46').c
+hr(hex '00');
my $recref_mp_fid = $segref->store_record('MP_FORMAT_IDENTIFIER', 
                                          $ASCII, 
                                          \$MP_FORMAT_IDENTIFIER, 
                                          4);

my $NEXT_IFD_OFFSET =
    chr(hex '42').
    chr(hex '00').
    chr(hex '00').
    chr(hex '00');

my $next_ifd_offset = $segref->store_record('NEXT_IFD_OFFSET', 
                                            $BYTE,
                                            \$NEXT_IFD_OFFSET,
                                            4);
#End of the MPIndex IFD
##########################################

##########################################
#write all the records to the segment buffer
$buffer  = $recref_mp_fid->get();
# ...
$buffer .= $next_ifd_offset->get();
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It does not matter if APP2 field descriptions are not supported. I only use your module to write chunks of data.