/usr/bin/jp2-thumbnailer is in openjpeg-tools 1.3+dfsg-4.7ubuntu1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71  | #!/bin/bash
# FILE: jp2-thumbnailer -- 
# AUTHOR: Robin Cornelius <robin.cornelius@gmail.com>
# DATE: 08 June 2008
# 
# Copyright (C) 2008 Robin Cornelius <robin.cornelius@gmail.com>
# Copyright (C) 2003 W. Michael Petullo <mike@flyn.org>
# All rights reserved.
# 
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
OUT=/dev/stdout
USAGE="[OPTION]...
  -h, -?   print this message
  -i path  set the input path   [ $IN ]
  -o path  set the output path  [ $OUT ]"
while :;
	do case "$1" in
		-h | "-?" )	
			echo -e usage: ${0##*/} "$USAGE" >&2
			exit 1 ;;
		-i )
			IN=$2
			shift ;;
		-o )
			OUT=$2
			shift ;;
		-?* )
			echo "${0##*/}: unrecognised option: $1" >&2
			exit 1 ;;
		* )
			break ;;
	esac
	shift
done
# We need to determine what type of jpeg2000 we can be either a codestream
# or an actual jpeg2000 file
#j2k_to_image is a bit dumb and makes its decisions based on file extension
# we can help it here with file -i
mime=`file -i $IN | sed "s/^.*: //g"`
if [[ $mime = "image/jp2" ]]
 then   ext="jp2"
else
	ext="j2k"
fi
temp=`mktemp -p /tmp`
cp "$IN" "$temp.$ext"
/usr/bin/j2k_to_image -i "$temp.$ext" -o "$temp.bmp"
rm "$temp.$ext"
mv "$temp.bmp" "$OUT"
 |