1. Albus Percival Wulfric Brian Dumbledore
Perhaps, this is the most obvious change in characters. Well, it was really unfortunate that Richard Harris (left) died after filming the Chamber of Secrets. I really liked his portrayal of Dumbledore because he was definitely calm and assuring. But while I can't say the same qualities on Michael Gambon's (right) portrayal of the role, I have to admit that he did a good job in making something, which not many could have realized if J.K. Rowling didn't tell the director about it, very obvious. His antics were indeed convincing, and somehow, I loved it.
2. Tom (of the Leaky Cauldron)
When Hagrid first brought Harry to the Leaky Cauldron (on their way to the Diagon Alley) during the Philosopher's Stone, Tom (left) looked rather normal looking. But on the Prisoner of Azkaban, Tom (right) was portrayed as a hunched, bald, and mischievous-looking wizard. Well, okay, the name of the one in the right photo wasn't mentioned but according to the books, the Minister of Magic was actually talking to Tom of the Leaky Cauldron. So I assumed... Oh well. I preferred the man they showed in the first film. The one on the third looked liked he came from the Knockturn Alley.
3. Professor Flitwick
I know they're both portrayed by Warwick Davis (and he's also Griphook!) but it's just fun seeing the changes on the appearance. In the first film, he looked like a mini-version of Dumbledore. Then, he decided to get a little makeover. This perhaps required him to drink a hair-growing potion, don't you think? I honestly preferred the one in the right, don't you?
4. Fat Lady
I personally prefer the second Fat Lady (right) than the first one (left). Well, okay, the first one was much regal-looking as how I would have expected when I first read the first book. But then, I think the younger one portrayed the role better. I mean, she was more fun; and she seemed like the one who would talk (and gossip with a friend!).
5. The Grey Lady
Okay, so nobody said the first ghost (left) was actually the Grey Lady; but since she came out after Nearly Headless Nick with the Bloody Baron in the first film, I assumed she was the Ravenclaw ghost. If she is, I would gladly choose the second Grey Lady (right) than her. She's beautiful and the emotions in her eyes convinced me that she was really Helena Ravenclaw who was killed by the Bloody Baron many centuries ago.
FIRST PHOTO: This young man was the one with Malfoy and Crabbe in front of the Shrieking Shack when Harry did pranks on them while under the Cloak of Invisibility (Prisoner of Azkaban). Well, the scriptwriters had twisted the plot on this part, perhaps; because on one similar incident, it was supposed to be Goyle in there.
SECOND PHOTO: We all know that Crabbe and Goyle were the ones who Malfoy was with during the fight with our trio inside the Room of Requirement (Deathly Hallows); but in the film (Part 2), it was Blaise Zabini who was with them.
Well, I'm trying to figure out more things to share. If you, guys, have anything to share, feel free to comment! :)