Matt reported that PHP crashs using imagecreatefromjpeg() - that's true and it took me a lot of time to find the error - but not only the Canon PowerShot S70, also the Canon PowerShot  A400 lets PHP (5.1.2) crash, without any chance to catch it!

So I exclude all Canon PowerShot images with the following check:

    function check_canonpowershot($filename) 
    {
        if (strpos(file_get_contents($filename), 'Canon PowerShot') !== false) 
        {
            return true;
        }
        return false;
    }