str_replace linebreaks and missing whitespaces

[GNDI]

I do a lot of thumbnails on my forum. But it looks messi because not all users are using the same syntax in there posts. Therefore I came up with this idear:

PHP Code:

$text = str_replace("[/img][/url][url]", "[/img][/url] [url]", $text);
$text = str_replace("[/img][/url]\n[url]", "[/img][/url] [url]", $text); 

But where to place the code....... I havetried several places but nothing worked out for me

Can anyone help me? and if so, could you make it as a product?