Active link under every image in concrete category of my blog

My blog contains about 1000 images, each article features about 10 images. I wanted to add an active active one link (www.google.com for instance) after each image on my blog in every post and category. I made it in functions.php by inserting such thing:

add_filter(‘the_content’, ‘superlink’);
function superlink($content){
$url = ‘google.com‘;
$content = preg_replace (‘|<img.*?>|iu’, ‘$0’.$url, $content);
return $content;
}

It works properly. But the thing is, I want to make this link appearing in only one category, so I made up this one:

add_filter(‘the_content’, ‘superlink’);
function superlink($content){
if ( is_single() && in_category(‘1234’){
$url = ‘google.com‘;
$content = preg_replace (‘|<img.*?>|iu’, ‘$0’.$url, $content);
}
return $content;
}

…it doesn’t work. Where I have made an error? Hope you can help me out.

Best,

Jack