find sub {
  # first filter out your directories
  if (-d && $_ !~ / my_target_dirs_regex / ) {
             $File::Find::prune = 1;
              return;
     }
  
#  if you make it to here, you are in your target subdir
# now do your ImageMagick processing and mkdir
# it has to check each file for a .png ending
if (-f && $_ =~ /  (.*)\.png$ / ) {
       
          # do mkdir stuf
          # do ImageMagick stuff             

     }

# or you could just push the files into an array for later processing
# push @goners, $File::Find::name;

   }, @ARGV;