I am using the Graph API Explorer with permission "friends_photos" and able to access some of my friends' albums, but some are not.
e.g.
/johndoe?fields=albums
Since my friends are not aware of my app, so I guess they should have some settings applied so I cannot access their albums even I have the "friends_photos" permission used.
I am able to access their albums using the web interface. Where is the settings?
It should work perfectly unless a user has disallowed the apps to access a particular category of his/her personal information.
People on Facebook who can see your info can bring it with them when they use apps. However, a user can control the categories of information that people can bring with them when they use apps, games and websites.
You can find these settings under Account Settings -> Apps -> Apps others use. It will give a menu for choosing a particular type of information that apps can access. Something like:
As you can see, it's possible for a user to stop an app from accessing his/her photos. However, the photos will remain visible using the normal web interface.