Here's an approach based on the iterator nature of a DBI statement handle:

my $sth = $dbh->prepare("SELECT id, filename, title FROM pictures");
$sth->execute();

print "<table ...>";
for my $row (1..$nrows) {
  print "<tr>";
  for my $col (1..$ncols) {
    print "<td>";
    my $pic = $sth->fetchrow_hash;
    if ($pic) {
      # emit html for the image
      # data for the picture is in hashref $pic, i.e.:
      # $pic->{id}, $pic->{filename} and $pic->{title}
    } else {
      # emit html for an empty cell
    }
    print "</td>";
  }
  print "</tr>\n";
}
print "</table>\n";
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Note that there is no need to compute the number of empty <td> elements to create - the return value of fetchrow_hash (either a hashref or undef) will indicate what should go in the cell.