I have not heard of a passholder discount, but a early purchase discount is available when you purchase 14 days in advance. Here is the information for Disneyland found here:Special Offers.
With PhotoPass+ you enjoy:
Unlimited PhotoPass photos in your account
The ability to customize your photos with fun Disney borders
Magic Shot photos
Photos from select dining locations
Photos from select attractions
Photos from other Disney experiences
Your Disney PhotoPass+ card for Photographers to recognize
By purchasing at least 14 days
before your vacation you pay
only $69.95 Order Now Compared to $99.95
Here You Leave Today and Enter the World of Yesterday, Tomorrow, and Fantasy.
“To all who come to this happy place; welcome. Disneyland is your land. Here age relives fond memories of the past...and here youth may savor the challenge and promise of the future. Disneyland is dedicated to the ideals, the dreams and the hard facts that have created America...with the hope that it will be a source of joy and inspiration to all the world.” - Walt Disney, Disneyland Opening Day Speech 1955