PHP 3.0.6 as Apache-1.3.3-module, MySQL module, magic_quotes_gpc compiled in. This is the first time I'm able to crash PHP :)

The following line produces the crash:
$img = str_replace("/usr/local/www", "", $img);

$img is set to "/usr/local/www/swc/image.jpg"

httpd-error.log:
httpd in realloc(): warning: chunk is already free.
[Tue Jan  5 12:00:17 1999] [notice] httpd: child pid 24100 exit signal Segmentation fault (11)