# prequery to see if there IS a previous/next id
  my $data = qq(SELECT id, title FROM pictures WHERE category = $category ORDER BY id ASC);
  my $sth = $dbh->prepare($data);
  $sth->execute() or die $dbh->errstr;

  my @pictures_in_category;

  my ($picid, $pictitle);
  $sth->bind_columns(\$id, \$title);
  
  while($sth->fetch)
  {
    push(@pictures_in_category, $id);
  }

# real query for the one image you're viewing
  my $data2 = qq(SELECT id, filename, title, category, description, date, views, sensorisospeed, exposuretime, isospeedrating,
                lensaperture, flash, focallength, cameramodel, shutterspeed FROM pictures WHERE id=?);
  my $sth2 = $dbh->prepare($data);
  $sth2->execute($picture) or die $dbh->errstr;
...