User-821857111 posted
The cookie approach suggested by mgebhard is the most frequently used solution for applying this kind of limit. It has its pros and cons. It is pretty easy to code and doesn't require that the user is registered, but cookies are browser-specific. Most users
won't know, but savvy users could use multiple browsers on multiple devices to circumvent the limit.
The database approach requires more code, and it also requires that you can identify a "user", so registration would be required, even for the free service. However, unless users are allowed to create multiple accounts, this will prove more tricky to circumvent
and is therefore more robust from your point of view.
I wouldn't recommend the IP address approach. They are not necessarily static and can be shared by multiple users, so you might end up telling someone that they have used their quota even though they actually haven't visited the site at all that day.
