Facebook Fried Request Verification

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I remember when the first few month i used facebook, every time i add a friend request to some one, facebook require me to enter some verification, (a chapca verification )where facebook show some writing and i need to repeat it. Well i know it is quite annoying but it is for own good since it helps us to avoid spam. But after a long time, the verification proses is gone now. But it only happened to old member, at least to me and a few of my friend, new member still need to enter this verification. Is there any rules / info in facebook about this verification. When will it is gone? And do you agree about this friend request verification system? Thanks