I mean, most of the time once a day is renewed, or every time you change the IP.
Because, as you may know, the first time it is used you only have to click and the green check mark appears, but when you use it often, you have to choose the diferent images.
Is not this a weakness, or could be an exploit?
Just fpr protecting from attack from lots of bots logging in and causing a problem similar to a ddos. So captchas will slow down the not traffic if there is some. Mostly its what is done. Works well otherwise they won't do it.