Why couldn't Frank work out Voldemort's resemblance to his father, while Morfin could?

Question

When teenage Voldemort came to his mother's house, his uncle Morfin mistook him for his father Tom Riddle (at first sight) however Morfin and Tom rarely used to see each other.

Morfin pushed the hair out of his dirty face, the better to see Riddle, and Harry saw that he wore Marvolo's black-stoned ring on his right hand.

"I thought you was that Muggle," whispered Morfin. "You look mighty like that Muggle."

"What Muggle?" said Riddle sharply.

"That Muggle what my sister took a fancy to, that Muggle what lives in the big house over the way,"

There's a line in Half Blood Prince stating

Merope had got her dying wish: he was his handsome father in miniature

But Riddle's own gardener Frank couldn't make any connection between the two faces and told the police that a stranger was the only person he saw around.

Frank was stubbornly repeating, again and again, that he was innocent, and that the only person he had seen near the house on the day of the Riddles' deaths had been a teenage boy, a stranger, dark-haired and pale.

Frank was working for Riddle's ever since he returned from war. Why didn't he recognize his master's face double?

Answer 1

Frank likely only saw him from a distance.

Frank seems to have only seen the young Voldemort at a distance, so likely had not seen him closely enough to be able to see any resemblance between him and Tom Riddle Sr. who he worked for.

“But over in the neighbouring town of Great Hangleton, in the dark and dingy police station, Frank was stubbornly repeating, again and again, that he was innocent, and that the only person he had seen near the house on the day of the Riddles’ deaths had been a teenage boy, a stranger, dark-haired and pale. Nobody else in the village had seen any such boy, and the police were quite sure that Frank had invented him.”
_{^{- Harry Potter and the Goblet of Fire, Chapter 1 (The Riddle House)}}

Morfin Gaunt saw young Voldemort from much closer when he went to the Gaunt shack. Additionally, Morfin saw Tom Riddle Sr. when he was younger, so the resemblance between them would be more apparent to him.

Answer 2

Because Frank don´t know how Tom Riddle Sr. looks in his teenager years. Tom Riddle Sr. born in 1905, so he was 16 in 1921. Frank Bryce born in 1917, so he was 5 at the time Tom Sr. was 16. We know that Frank began to work for the Riddles after the Second War World, we don´t know if Frank knows Tom beforehand but unlike Morfin Frank couldn´t know how Voldemort´s father looks at 16.

Answer 3

Frank knew Tom Riddle Senior better as an older man than as a teenager

Voldemort was 16 when he killed his family. For Frank to recognise him positively as looking like his father, especially as he only said he saw him, but didn't speak to him, making it unlikely he saw him that close, he would have needed to recognise his father at a similar age (say 14-21 for argument's sake).

The film puts Tom Riddle Senior's date of birth in 1905 (just from the books it could be a bit earlier, but not much later, because he fathered Voldemort in 1926). So we're looking at the years of approximately 1919-1926.

We know Frank was born in 1917 (he's nearly 77 in Goblet of Fire, which is set in 1994). So we can probably say up to the age of 6-ish (1923) he probably wouldn't recognise or remember him that well, plus Tom Riddle would probably have been away at boarding school. From 1923-1926 he was potentially at university, which was reasonably common among young men from the landed gentry at that time.

Frank also lived in the village, again reducing the amount of time he'd have seen him — a lot of Tom Riddle's life would have revolved around the big house and the estate, rather than in the village.

We're also told that Frank had been working for the Riddle's ever since he came back from the war injured, so late 1939 at the earliest, making Tom Riddle Senior about 35. He's much more familiar with the older-looking Tom Riddle than he was with his as a teen.

Morfin on the other hand was much closer in age to Tom Riddle, and they lived nearer and often saw him riding by. He also had a particular reason to remember him in his late teens/early twenties — that was when he attacked him and was sent to Azkaban. I'd also hazard a guess that after returning to Greater Hangleton, Tom Riddle didn't ride out so close to the Gaunt's shack again, limiting the amount of times Morfin saw his as an older man (although that's speculation).