$counter = 0;
# add link text to each filename
foreach my $name (@filenames) {
  if ($counter % 2){      #odd rows
    $name = qq{<tr><td><img align="center" valign="center" src="TN/tn_$name" width="75" height="42">
    &nbsp;&nbsp;<a href="$name">$name</a></td>\n};
  }else{                  #even rows
    $name = qq{<td><img align="center" valign="center" src="TN/tn_$name" width="75" height="42">
    &nbsp;&nbsp;<a href="$name">$name</a></td></tr>\n};
  }
  $counter++;
}