With iOS 6, Apple has introduced a new privacy setting—you need to give explicit permission to apps that want to access your Camera Roll.
This is a substantial—and practically unannounced—change. In the past, any app could write to your Camera Roll while any app that wanted to read from it needed to have Location Services permissions enabled. This was because images and videos on Camera Roll can contain location-specific data. And, yes, it was confusing. The new option is more logical, but—thanks to users not being aware of its implications—is still causing problems.
The first time you try to take a picture or read from Camera Roll with a photo app after installing iOS 6 (or buying a new iPhone, iPad or iPod touch with iOS 6 installed) you will get an alert that looks like this:

Unless you select “OK”, the app will be unable to use Camera Roll at all—it won’t save images or let you view them. In short, it won’t work.
Troubleshooting
What do you do if you selected “Don’t Allow” by mistake?
That’s easy, fortunately.
Go to the main Settings app on your Sprinboard:

Select Privacy:

Select Photos:

And then make sure the apps you want to use are turned ON:

That’s all there is to it!

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