In OoTP movie, Harry is walking along the platform to return to Hogwarts when he sees Voldemort standing there wearing a black suit.Was Voldemort actually present or is it Harry's mind playing tricks?If he was present, did he come just to see Harry off?
This does not happen in the books. Now, putting away the book and focusing only on the movie, it is still clear that Voldemort did not come to the station:
- Only Harry seems to notice him. Remember that there are dozens of muggles and wizards transiting the station, and no one bats an eye. There's really no feasible way a whole crowd won't notice that handsome man in the middle.
- Voldemort doesn't do anything. Clearly he didn't come to kill Harry - so what then? See Draco off to school?
Since this particular book puts special emphasis on Harry's and Voldemort's "mental" link, it is very likely that this was nothing but a way to illustrate how Harry is starting to lose his mind.
Adding to what everyone said, it might be a sign of Harry's PTSD from the fight with Voldemort. During the whole movie he is showing signs of it, and seeing his attacker in the crowd for a moment are very normal symptoms of PTSD.
I think that Voldemort wasn't really there, but either Harry was going mad, was thinking about him and imagined him there, or he used his skills at Legilimency to make Harry imagine he was there and disturb him. Here is further information on the subject:
He was imagining it.
In the case of Harry thinking about him, he must've been going mad and/or thinking about him so much that he imagined him being right in front of him.
You-Know-Who used his Legilimency to let only Harry see him right there, because he wasn't exactly imagining it.
It is a very complicated subject, so don't worry if you don't understand. I don't completely get it either. I think I'll add more on my subject another time.
Voldemort doesn't actually arrive on the platform. He appears only as a figment of Harry's imagination. I believe this moment is symbolic of Harry's inner emotional struggle to convince the wizarding world of Voldemort's return. Earlier on, Dumbledore says the evidence of his return is incontrovertible yet nobody believes him or Harry. Even though Harry can see Voldemort in plain sight, nobody acknowledges him, leaving him to feel helpless in his efforts to shed light on the imminent danger that lies ahead. In addition, it's also a clever way of introducing the connection between Harry and Voldemort, as they share an ominous personal moment amidst a large crowd of people on the platform.