Factual error: In the first few scenes they show some newspapers. They show Tuesday April 10, 1899, then Thursday May 18th,1899. If April 10th is on a Tuesday, then May 18th can't be on a Thursday, it would be on a Friday. April 10, 1899 was actually a Monday, but May 18th that year was indeed a Thursday. (00:03:45 - 00:04:55)
Factual error: In a shot near the beginning of the film, the gravestone for Allan Quatermain's son is misspelled "Quartermain". [People are trying to correct this, saying the spelling's correct - no it's not: http://uk.imdb.com/Title?0311429.] (00:12:50)
Factual error: When the League arrives in Venice, Carnivale is being celebrated. In the film they leave London in July and arrive there a few days later, but in Venice, Carnivale is celebrated on the last weekend before Lent - which differs from year to year, roughly between early February and early March. (00:13:15 - 00:53:05)
Factual error: When M tells Allan Quatermain that he and his team have four days to go from London to Venice, he answers that this is impossible, and captain Nemo replies that it will be possible thanks to his science-fictional devices. Actually, on late 19th century railways, this trip would have taken less than two days. For example, the Peninsular Express departed every Friday afternoon from London, and it arrived at Brindisi, a considerably more distant town in southern Italy, on Sunday afternoon. (00:16:39)
Factual error: In Venice, Quatermain hunts down M in a cemetery, only there is no cemetery in Venice. The burial ground is on the island of San Michele in the lagoon. (01:01:25)
Factual error: Quatermain sits in the snow for hours, without gloves, holding a rifle with substantial metal parts, yet his hands don't freeze onto it or (presumably) get frostbitten. (01:16:55)
Factual error: Apparently, Captain Nemo's submarine, Nautilus, is a shape-shifter. When it first surfaces next to the dock, it appears to rise easily 100 feet above the water, and that's only the visible part of the submarine; the bulk of the craft is still below the surface. This suggests that the water is a good 300 feet deep or more right off the dock, which is impossible. At this enormous size, it's also impossible that the Nautilus negotiates inland waterways, as when she goes to Mongolia. Strangely, we also see an overhead shot in which the Nautilus appears to rise only about 40 feet above the surface (compared to three-storey buildings directly adjacent).
Factual error: How did they get the Nautilus up the Thames? Or into Venice? They'd have had to dredge the river to get it into London. Also, what's really under Venice? I thought Venice was built on a marsh, why would there be all those nifty tunnels and columns under there, why not just foundations and such?
Factual error: In Kenya, Alan Quatermain pushes a guy back with a table and impales him on a horn on the wall. The table hides the wound, but the horn punches through. If this guy was impaled on that horn, it would have some blood on it. However, it's just as totally clean as it was before.
Answer: I haven't read this book of Wilde, but I think alterations were prompted not by copyright issues but because this conveniences the "league" storyline.