PHP: Human Readable Random String

This code will create a human readable string that will look more close to dictionary words, useful for captchas.

function readable_random_string($length = 6){  
    $conso=array("b","c","d","f","g","h","j","k","l",  
    "m","n","p","r","s","t","v","w","x","y","z");  
    $vocal=array("a","e","i","o","u");  
    $password="";  
    srand ((double)microtime()*1000000);  
    $max = $length/2;  
    for($i=1; $i<=$max; $i++)  
    {  
    $password.=$conso[rand(0,19)];  
    $password.=$vocal[rand(0,4)];  
    }  
    return $password;  
}