Andrew, I've got photos of seven or eight candidates, all with some claim to authenticity and none of them positively identified by members of Titanic's crew. Some were taken on in the area of the sinking on the morning of April 15th. I find none of them truly credible. The one known as the Rehorek berg is described on this site. It has the merit of being possibly the right shape, with a roughly vertical face that would throw ice on the ship's deck. It's weakness is that the photo was taken well after the sinking.
The one in ANTR has no real claim at all. It was taken well after the event and the red paint story seems rather unlikely.
The real truth is that we just don't know who dunnit.
What I just thought is that maybe the iceberg broke into a different pieces. Is it possible that all the icebergs we see might be pieces of the original iceberg that collided with Titanic?
In the book "Unsinkable" the author writes that there was a smear of red paint on the iceberg I show above, and that is why it is believes to be the one that Titanic hit; in other words, they are pretty certain that it at least collided with something.
"the smear of red paint" story is highly dubious:
1) Grab a block of ice and try scratching some cars in the neighborhood with it!! (for a cheaper alternative try abandoned cars, car graveyards, etc) and see for yourself how unlikely it is for paint to smear on ice.
2) The red-painted sections of Titanic's hull were usually underwater hence that's exactly where the red smear of paint would have been. Therefore not visible to people who took the photo.
Bottom paint is not like the hard stuff put on cars. It is a soft paint designed in part to "slough" away in use. It might well have rubbed off on the iceberg especially considering the forces involved.
As far as the paint smear being above water, that is also possible. Titanic must have done some damage to the iceberg as ice has only a fraction of the crush strength of steel. It is entirely possible that contact with the ship changed the underwater shape and/or centers of gravity and buoyancy of the iceberg. This would have resulted in the berg rolling somewhat and possibly displaying some formerly submerged portion.
At least two ships ran afoul of icebergs in that area during the same week: Titanic and Niagara. There may have been others that made port without incident. So, the stain may be real bottom paint but that does not mean it is necessarily from Titanic.
I believed for years that the Adalbert berg was probably the culprit, until I tried to reproduce it in styrofoam the same scale as my Titanic model. The area that features the scar of paint appears curved inward, and I completely fried my brain trying to get the Titanic's hull into that shape. Suffice to say, I abandoned that berg as the bad guy.