можно первый пост загрузить с темы
{{$post = $topic->topic_firstpost ? \IPS\forums\Topic\Post::load($topic->topic_firstpost)->post : NULL;}}
{{if $post AND \preg_match( '#<fileStore.core_Attachment>\S+(?:jpg|jpeg|png|webp)#', $post, $image_url )}}
{{$image_url = \str_replace('<fileStore.core_Attachment>', \IPS\File::getClass('core_Attachment')->baseUrl(), $image_url[0]);}}
{{if settings.lazy_load_enabled}}
<a href="{$topic->url( "getPrefComment" )}" title="{lang="read_more_about" sprintf="$topic->_title"}" >
<img class='ipsImage' src='{expression="\IPS\Text\Parser::blankImage()"}' alt='{wordbreak="$topic->_title"}' data-src='{file="$image_url" extension="core_Attachment"}'></a>
{{else}}
<a href="{$topic->url( "getPrefComment" )}" title="{lang="read_more_about" sprintf="$topic->_title"}" >
<img class='ipsImage' alt='{wordbreak="$topic->_title"}' src='{file="$image_url" extension="core_Attachment"}'></a>
{{endif}}
{{endif}}