You will need to set up a merchant account/gateway to do this but it's quite easy to pre-authorize[1] a card for a small amount - $1.01 or some such and then never capture the payment. That way, you verify the account is valid and active and passes CVV and AVS yet you don't actually collect any money.
I assume you'll be charging people eventually otherwise I'm guessing your processor won't be too happy about you only pre-authing transactions.
[1] A note about debit cards used pin-less: When you pre-auth a credit card, a hold is placed on the money until you either capture it or the hold falls away (usually after a few days). BUT when you pre-auth a debit card the money is actually taken out of the checking (or whatever) account tied to the card. It will only be returned if the hold expires.