I'm trying to comprehend the general mechanism utilized by certain websites to permit non-registered customers or just visitors to election for something (e.g. reviews, videos, images..etc). How can they keep an eye on that? As with websites like these, exactly the same guest can't election two times in the same terminal. Will they store their IP addresses? or they save the pc ID/title?

Any ideas are greatly appreciated.

P.S: (mywot.com) is a good example of websites like these.

They will use snacks or periods to recognize the pc, which has already chosen. Should you understand Javascript or PHP a little, I can provide you with some good examples.

EDIT: OK, so here's a good example:

<button value="VOTE" onClick="vote();">
<script>
var votes = 9654;  //Some vote counter - only for test purposes - practically, this wouldn't work, the votes would have to be stored somewhere, this number is only stored in the browser and won't actually change for everyone, who sees the page!
function vote()
{
 var cookies = document.cookie.split(";"); //Make an array from the string
 var alreadyVoted = false;
 for (var i = 0; i < cookies.length; i++)  //Iterate through the array
 {
  temp = cookies[i].split("=");
  if (temp[0] == "voted" && temp[1] == "true")  //The cookie is there and it is "true", he voted already
   alreadyVoted = true;
 }
 if (alreadyVoted)
 {
  alert("You can't vote twice, sorry.");
 }
 else
 {
  var date = new Date();
    date.setTime(date.getTime()+(5*24*60*60*1000));  //Cookie will last for five days    (*hours*mins*secs*milisecs)
    var strDate = date.toGMTString();  //Convert to cookie-valid string
  document.cookie = 'voted=true; expires=' + strDate + '; path=/';  //Creating the cookie
  votes++;  //Here would be probably some ajax function to increase the votes number
  alert("Thanks for voting!\nVotes: "+votes);
 }
}
</script>

Hope this can help, but it is only a simple cookie demnostration code and really wouldn't work with voting! You would need to apply certain PHP or something like that much like really keep election values...

The typical technique is by using snacks. IP addresses isn't enough because lots of places nowadays use NAT (offices, cybercafes, most houses with DSL hubs).

The snacks should ideally be processed within the back finish but may also be processed in javascript within the browser.

Snacks truly are the answer. Here is a system that will work:

Possess a votes table within the database recalling the votes for every customer ID. Whenever a customer enter your website, see if the request consists of a customer_id cookie. Otherwise, then produce a unique customer_id (utilizing a uuid generator), and set a customer_id cookie within the response, using the produced id as value. This cookie ought to be made persistent.

Every time a election is triggered (and/or every time you produce a election link), see if the present customer, recognized by his customer_id cookie, has chosen or otherwise because of the votes table. Whenever a election is performed, store it within the votes table.

Obviously, nothing stops any customer to obvious its snacks, in order to use another browser or machine to election several occasions. But without authentication, this is the best that you can do.