The Student Room Group
Obviously anything the user is asked to enter or select would be overt - e.g. product/quantity/address etc.

I wouldn't have said cookies were a method of capturing information but simply storing/retrieving information. They are covert to some extent as most people don't know or care about a site setting a cookie but some users can set up their browser to warn about cookie or just reject them.

Covert could be things like IP address, browser info, OS info, screen resolution etc. - things that the user isn't specifically asked for. However, all of those things with the exception of the IP address can be faked or withheld if the user wanted to.

HTH