image verification makes every bot not be able to log itself in. Now a human has to do it for them instead. This barely slowed down botting like 1% because in the morning botters just log in all their bots manually by solving the verifications themselves.
E-mail verification in this case means they'll send out an e-mail to the address you give them when you sign up for a new account. The e-mail has a link saying "click here to activate your account." You can't log in with your new account until you verify it that was so basucally you have to give them an actual, functioning e-mail address that you can check. This is supposed to prevent people from signing up 100 bot accounts really fast because if you try and use the same e-mail address for the 2nd one you sign up, it will say that one is already in use. Who has 100 e-mails addresses, right? Wrong, that system doesn't work at all as I pointed out here:
http://www.silkroadforums.com/viewtopic.php?p=462618#462618