It doesn't exist. Can say that confidently. If it existed we'd have been following it for centuries on its thousands of years path into the inner solar system.
Planets can't just jump into the inner solar system without being seen, hide behind the sun, then jump out at us like a demented gazelle :). The supposed images of Nibiru are just lens flares. Cheap lenses especially show extra images of the sun just next to them.
If you think you've spotted Nibiru by photographing the sun - the thing to do is to put your finger in front of the sun, between your camera and the sun. You should spot that your "Nibiru" disappears. And if you put your finger in front of Nibiru, or try, you will see that Nibiru appears between your finger and the camera. It's just an internal reflection in the camera lens.
And try searching the last year's photos on Flickr for Nibiru
These are photos taken by people who usually have decent quality equipment and lots of photographic experience.
And anyway - do you think that a planet easily visible in photos of the sun could be hidden somehow from all the tens of thousands of amateur astronomers world-wide? It makes no sense if you have just a little bit of astronomy background. A day time visible comet next to the sun would be top astronomical news, cover photos in all the astronomy magazines and tips about how to observe it.