On my Dec trip Disney had just shut the down the old link that had the discounted pre-purchased CD for $99. They are now email codes to guests staying onsite.
The link to pre-order is 'hidden' in an email about all the great things to do at on your trip. It arrives sometime around 45 days prior to your trip (or closer to your trip). The email had a little blurb about photopass - it says NOTHING about a discount, when you click on the icon in the email it takes you to a page when you may pre-order for $99. Do not click on it until you are ready to order, some people reported that if the clicked on the link and then closed the window they were unable to get the pre-order offer again.
If you don't receive the email 10 days prior to your trip you may email or call Disney Photopass to request the pre-order.
HTH!