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 $image = new Image::MetaData::JPEG($ARGV[0]);

# This would be the correct procedure for adding records at low level
# if the APP2 update routine existed at all (but it isn't implemented)
# 1) create an empty APP2 segment
#   my $segref = 
#      new Image::MetaData::JPEG::Segment('APP2', undef, 'NOPARSE');
# 2) store a record with a given key and value
#   my $head = "MPF0";
#   $segref->store_record('MP_HEADER', $ASCII, \$head);
# 3) IMPORTANT: update the binary block from the in memory
#    representation (this was the step you were missing)
#   $segref->update();

# But APP2 can "currently" only be parsed if it contains Flashpix
# conversion information ("FPXR") or ICC profiles data. And there is 
# no update routine at all. So, either you extend the package or
# create the entire binary block by hand in a local variable: 
# you skip parsing and just create the segment.
my $buffer = "MPF0\0";
my $segref = 
   new Image::MetaData::JPEG::Segment('APP2', \$buffer, 'NOPARSE');
# then insert it into the image 
$image->insert_segments($segref);
# the segment is there, albeit without description, since unparsed
foreach my $s ($image->get_segments('APP'))
   { print $s->get_description(); }
# you can save to file nonetheless, unparsable segments aren't dropped
my $new_file_name = 'tmp1.jpg';
$image->save($new_file_name);
print "---------------------------------\n";

# now open the new file and check that APP2 is there (I avoid trying
# to parse it, since parsing would fail with "Invalid APP2 segment"
# in this case)
my $new_image = new Image::MetaData::JPEG($new_file_name, 'APP[^2]');
foreach my $s ($new_image->get_segments('APP'))
   { print $s->get_description(); }
print "---------------------------------\n";

# have a look at what's really inside your file: the APP2 segment
# should be in the very first lines, unless your APP1 is huge.
use Data::HexDump;
my $hexdumper = new Data::HexDump;
$hexdumper->file($new_file_name);
$hexdumper->block_size(1024);
print while $_ = $hexdumper->dump;