If you're in the picture, you know the facts about what's happening. It's often used with the verb 'to keep', as in the examples below.
Jane kept me fully in the picture so I knew what to expect when I attended the meeting.
Please keep me in the picture. I need to know how the project is going.
I'm not really in the picture any more when it comes to the news. I've stopped reading newspapers.
If you're out of the picture, you're not important, involved or necessary in a certain situation.
Bob's out of the picture for this job, he's been off sick for weeks.
Sadly she's out of the picture. Her English isn't good enough.
A drawing, painting or photograph can also be described as a picture.
In America, a picture is also another name for a film.