our KEY_LIST => [ qw/
    thumbnailForWebsite
    thumbnailForForums1 thumbnailForForums2
    hotlinkForForums1 hotlinkForForums2
    hotlinkForWebsite
    showImage
    directLinkToImage
/ ];
sub get {
  my $self = shift;
  my $key = shift;
# could grep @{&KEY_LIST} here too to check for valid key
  return exists $self->{liste}->{$key} ? $self->{liste}->{$key} : undef;
}
# this could be left the same or changed to this:
sub get_all {
  my $self = shift;
  return { map { $_ => $self->{liste}->{$_} } @{&KEY_LIST} };
}
# note: could also replace get_all() with get() or get('all')

# and note that the loop in upload() becomes just:
  foreach( @{&KEY_LIST} ){
    ...
  }