IPhone view all photos ever sent/received?

I heard there's a way to access all of the photos you've ever sent/received on an iPhone. Like via iMessage or something. It takes up "other" memory, and if you plug in your phone you can do something to view all of those photos?

Open your photos app then go to photo stream.

I don't believe it. What if the "other" memory gets filled up?

If the pictures don't appear anywhere in your Photos app, they aren't on your phone anymore.

Not true. There are pictures in your text messages that are still there and is taking up space!