Hello everyone..

How can i prevent users to make several accounts on my website with php?

simply i want to make sure that from each computer only 1 account is created ?

i tried IP nd cookies... but ppl will use proxies and delete their cookies.. and they will join again...

Thx

There truly is no way to stop it. You can put in as many preventative measures as possible to stop the average user. Such as cookies, REMOTE_ADDR get their ip, require an email address and have a link sent to that email that they have to click on and confirm. Of course all these are easy to get around - use proxy, delete cookies, get a free email from yahoo etc... But the more preventative measures you have in place the more duplicate users you will thwart. You could require people to sign up with a non-free email address, but that may prevent some potential users from signing up for the first time.
There is no way (with php or any other language to prevent people from signing up anywhere twice) You can do like ebay and require personal info and that would stop alot, but again I've had around 5 different ebay accounts so there really is no way to 100% prevent anyone from signing up more than once.

Inet411 is completely right. The best thing to do is:

1) Log IP and check for duplicate
2) Log email and send confirmation
3) Use image verification
4) Hope all goes well

The question here becomes not how to prevent multiple registrations but how to mitigate any damage caused by it.

For example, if it is an issue of people registering for a contest then you require names and addresses. Check for duplicates in the db upon registration. Then make it known in the rules that when the winner is selected you will confirm the name and address given. If the name or address is invalid the entry is disqualified and you pick another. You can't prevent multiple entries but this way you can ensure that one alone is valid.