#!/usr/bin/perl
use strict;
use warnings;
use Gnome2::GConf;

my $imgdir='/home/topeg/.BILDER/';
my $gpath='/desktop/gnome/background/picture_filename';

my $client = Gnome2::GConf::Client->get_default();
my $img=$client->get_string($gpath);
my @imgs=sort glob("$imgdir*.*");

my $cnt=0;
while($cnt<@imgs)
{
  last if($img eq $imgs[$cnt]);
  $cnt++;
}
$cnt=-1 if($cnt>=$#imgs);
$cnt++;
$img=$imgs[$cnt];

$client->set($gpath, { type => 'string', data => $img });