white.jpg is the file to be given to the players. flag.jpg is the solution,
obtained by some simple hex editing (get_flag.py will create flag.jpg given
white.jpg) to make some padding visible. solution.md contains an
explanation of how the challenge works.
white.jpg was generated by creating a 528x512 image in GIMP, then using
convert as follow:
convert gimp.png -sampling-factor 3x1,3x1,3x1 -type truecolor white.jpg
and finally reversing the edit done by get_flag.py.