This function implements a comparison algorithm that orders alphanumeric strings in the way a human being would, this is described as a "natural ordering". An example of the difference between this algorithm and the regular computer string sorting algorithms (used in strcmp()) can be seen below:
$arr1 = $arr2 = array("img12.png","img10.png","img2.png","img1.png"); echo "Standard string comparison\n"; usort($arr1,"strcmp"); print_r($arr1); echo "\nNatural order string comparison\n"; usort($arr2,"strnatcmp"); print_r($arr2);
Standard string comparison Array (  => img1.png  => img10.png  => img12.png  => img2.png ) Natural order string comparison Array (  => img1.png  => img2.png  => img10.png  => img12.png )
Similar to other string comparison functions, this one returns < 0 if str1 is less than str2; > 0 if str1 is greater than str2, and 0 if they are equal.
Note that this comparison is case sensitive.