Effective way to implement the number of views on images - PHP -

i've created website users can upload images , i'd record total number of views individual image.

now idea on implementation this:

store ipaddress of visitor in session, fe:

$key = "view_img_".$img->id;   if(!isset($_session[$key]))   {      $_session[$key] = array();   }    $visitoripaddress = $_server['remote_address'];    $found = false;    foreach($ip in $_session[$key])   {    if($ip == $visitoripadress)      {         $found = true; //visitor has visited before in livespan of session         break;      }   }    if(!$found)   {      //do sql update query number of views image      $sql = mysql_query("update ") //etc.       //add ip list in session      $_session[$key][] = $visitoripadress;   }   

now problem this:

i'd clear visitor's ipaddress inside $_session[$key] variable after timelimit clear resources.

the thing is:
of visitors might view image once, , when image gets old might not visited longer, session still exist.

is there way define lifespan specific $_session variable resets itself? (equal $_session[$key] = null)

or there better way implement this?

what counting via sessions approach number of unique views. if want count number of views, don't put brain , run query like:

update counttable set views = views + 1 imageid = 123 

populate imageid , you're go. kiss.