Сниппет проверки наличия содержимого.

<?php
$TVname = isset($tv)?$tv:'catimg#';
if( $TVarray = $modx->getTemplateVarOutput(array($TVname)) ){
$tvOutput = $TVarray[$TVname];
if(empty($tvOutput)) return '';
return '<img src="assets/images/catalogimg/[*catimg#*].jpg" height="120" width="155" border="0"  alt="[*pagetitle*]" />';
}
return '';
?>

<?php
$id = isset($num) ? $num: '1';
$TVname = isset($tv)?$tv:'catimg' _ $id;
if( $TVarray = $modx->getTemplateVarOutput(array($TVname)) ){
$tvOutput = $TVarray[$TVname];
if(empty($tvOutput)) return '';
return '<img src="assets/images/catalogimg/[*catimg' _ $id _ '*].jpg" height="120" width="155" border="0"  alt="[*pagetitle*]" />';
}
return '';
?>