<?php
$regex = '~
            (\h*\(                            # capture groups, open brackets
                .*?                           # match everything lazily
                (?:(?i)picture|see|lorem(?i-) # up to one of the words, case insensitive
                .*?                           # and anything lazily afterwards
            \))                               # up to a closing bracket
            ~x';                              # verbose modifier

$text = array();
$text[] = 'Hello world (see below).';
$text[] = 'Lorem ipsum (there is a picture here) world!';
$text[] = 'Attack on titan (is lorem) great but (should not be removed).';

for ($i=0;$i<count($text);$i++)
    $text[$i] = preg_replace($regex, '', $text[$i]);

print_r($text);
?>