While a lot more can be said about this topic, This answer by u/Hazeltin includes a discussion of islets found via Satellite.

Landsat Island – a name bestowed by the Canadian Board of Geographical Names, and a discussion of which by u/Hazeltin is linked to elsewhere in this thread – does seem to be the sole recognised landmass, other than new volcanic islands such as Surtsey, off the coast of Iceland, to have actually been discovered by satellite imaging. Actually, referring to Landsat as a landmass is a bit of a stretch – it measures 50 yards by 25 and stands about 35 feet clear of the surface of the North Atlantic eight miles east of House Island, off the coast of Labrador.

But it's also worth noting that the simple fact that satellites exist has not definitely settled the question of whether other small islands may not still exist undiscovered. Most satellite cameras are pointed at known civil and military targets, and those that do scan the oceans produce millions of images that have never been comprehensively scrutinised for what they may reveal.

Indeed, at least one other potential discovery which postdates Sputnik but has yet to clear the bar in terms of general recognition occurred in 1979 in the southern Indian Ocean, where a US aircraft carrier group reported the discovery of a new reef 9 miles east of Diego Garcia. The discovery was confirmed in multiple ways at the time – visually from the ships in the group, by helicopter, and by both fathomometer and leadline – and the admiral insisted on it, but two subsequent searches by professional hydrography teams failed to confirm it.

Perhaps just as interesting, however, is the long-running presence on nautical charts of a plethora of "doubtful islands", marked with the notation "E.D." ("existence doubtful") or P.D. ("position doubtful"), several of which have been sighted and charted on several different occasions, but the existence of which cannot now be confirmed by modern technology.

The most famous of these doubtful landmasses are probably the Auroras, in the South Atlantic, a group of three supposed islands originally discovered by the crew of a ship of that name in 1762, rediscovered in 1790, and professionally surveyed in 1794 by the Spanish survey vessel Atrevida. No sign of these islands has been reported since. Much the same can be said of the mysterious Thompson Island, supposedly a small, low-lying mass located to the north east of Bouvet Island, sighted in 1825 and sporadically thereafter until 1893, which features heavily in the 1962 novel A Grue of Ice, by Geoffrey Jenkins. Whether these islands ever existed, but were destroyed by volcanic activity, or whether they were actually large icebergs, remains a matter of dispute.

Not all such doubtful islands have been reported anywhere near the poles, however. The most recent notable case involves an island known as Bermeja, in the Caribbean off the Yucatan peninsula, which appeared on maps from the 1500s and was charted by Mexico in 1941. Air-sea searches conducted early in this century failed to confirm its existence. Campbell, writing in 2009, reports that as of that date Bermuja's co-ordinates still appeared in the CIA world handbook and on Google Earth, but a search for Bermuja in that year failed to reveal any trace of the island – a matter of some importance to the Mexicans, since confirmation of its existence would extend their territorial waters by about 55 miles in a region known to be rich in mineral wealth.

One final point is that doubts about many of these islands persisted largely because they were so far off normal shipping lanes. Gould makes the point that the Belcher Islands, in Hudson's Bay – an archipelago of 1,500 islands, some of which are 70 miles long and almost within sight of the mainland – were not discovered (by Europeans - though they were well known to the Inuit) until 1915, even though the Bay itself had been known and regularly traversed by British and French ships ever since 1610, simply because they were not on any shipping lane.

Sources

Matthew Campbell, "Oil boom fuels mystery of the missing island," Sunday Times 6 September 2009

David Cuen, "Mexico's missing island," (BBC World Service radio documentary, 11 September 2009)

Rupert Gould, "The Auroras, and other doubtful islands", in Oddities: A Book of Unexplained Facts (1928)

Henry Stommel, Lost Islands: The Story of Islands That Have Vanished from Nautical Charts (1984)

Can there be some clarification on the question? Does OP mean undiscovered islands, land that's part of discovered territories but unmapped, or maybe even geographical features covered under foliage (such as those newly discovered Mayan cities).

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