Missing pictures after changing Apple ID

You can also try signing back into the old ID and turn on iCloud syncing. When all of the data is recovered, change to the new ID. When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion. If possible, also set up Family Sharing  between the IDs to keep access to your apps/purchases. 

 How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.       

What to do after you change your Apple ID or password - Apple Support.      

Family Sharing of Photos - "When you set up your family, a shared album is created automatically in the Photos app on all family members’ devices. Everyone can add photos, videos, and comments to the album whenever they like and get notified when something new is added."

From: http://www.apple.com/icloud/family-sharing/

It sounds to me like you need to get the owners of the other ID to move your missing photos to the shared album.