There's no automatic delivery possible with this kind of Paypal integration, because the skin is not capable of verifying if the payment was successful or not. You have to provide (secret) links on your server after you've received the notification from PayPal.
I have no idea if this could be automated at all. A mail comes from PayPal which notifies you of the successful payment. Now what should happen? jAlbum and the skin can't read your mails.
Professional shopping carts run on the server, they can communicate with the payment provider (PayPal) and they can prepare images in a secret folder and send a link to the customer. This lightweight integration in Tiger does require human intervention, sorry. Professional shopping cart solutions can cost hundreds of euros per month - not the same league as jAlbum.