Some have argued that while Vettel technically left Karthikeyan enough room on the track, that he was still in the wrong because they believe he cut Karthikeyan on the racing line. There also appears to be some confusion on whether Karthikeyan was off the track/on the white line or not.
Whose right is it to take the racing line?
First of, as the car lapping the other driver, Vettel had the right to take whichever place he wanted on the track, as long as he leaves the backmarker enough room. At their positions in frame 5, Karthikeyan has enough room to continue on the track.
At that point, Karthikeyan has the opportunity to let Vettel pass, which he needs to do as stipulated in the sporting regulations:
“20.5 As soon as a car is caught by another car which is about to lap it during the race the driver must allow the faster driver past at the first available opportunity.”
Did Karthikeyan turn in to take the racing line?
However, there are still some that want to interprete that as not meaning Karthikeyan did not have the right to keep the racing line. So that beckons the question: was Karthikeyan turning in to take the normal racing line, as the Marussia is seen doing in front of them?
Short answer: no. Although the camera pans, taking two static points allows us to compare the racing lines. The orange line shows where (the left rear wheel of) the Marussia starts moving right, away from the edge of the track. In the second frame, you see Karthikeyan starts moving right almost a full car length earlier, despite the fact Vettel is already mostly past him.
Was Karthikeyan returning on the track, or on the white line?
It happened quite fast, so I understand where that idea came from, but Karthikeyan actually went a little off just before the corner. He had already returned on track when going into the corner, and when Vettel was passing him, Karthikeyan was not on any white line.