WARNING: The following contains SPOILERS for Spider-Man: No Way Home
Spider-Man: No Way Home brought back several Spider-Man villains who battled Toby Maguire and Andrew Garfield's Spider-Man in their respective universes, and in the case of Sandman (Thomas Haden Church), it actually reused some footage from Spider-Man 3 to bring him to life. Thanks to some combination of a spoiler-averse production model, COVID-19 limitations on principal photography, and the complications of bringing back an actor 14 years after their last appearance, a number of creative techniques had to be utilized to bring Sandman, AKA Flint Marko back to the big screen, including the re-use of some of Sam Raimi's original Spider-Man 3 photography.
In Peter Parker's attempt to have Doctor Strange create a spell to make the world forget he's Spider-Man, he accidentally made the former Sorcerer Supreme mess up the spell, resulting in multiple villains who knew Spider-Man was Peter Parker crossing the multiverse to enter Tom Holland's MCU continuity. The villains included Dr. Otto Octavius (Alfred Molina), Green Goblin (Willem Dafoe), Electro (Jamie Fox), Lizard (played by Rhys Ifans in The Amazing Spider-Man, but uncredited in Spider-Man: No Way Home), and Sandman.
While it'll be impossible to properly compare footage until Spider-Man: No Way Home is released for home viewing, thanks to Sam Raimi's iconic camera work, it looks like several shots were repurposed from Spider-Man 3, specifically the shots after he's healed and turns back into Flint Marko. The editing is fairly seamless, but the iconic zoom-in on his face as he's rising out of the sand is clearly repurposed from the scene in Spider-Man 3 where he fights Tobey Maguire's Spider-Man in the sewer. There's only a few shots of him in his human form, so it's likely they're all repurposed from Spider-Man 3 footage.
Considering neither Thomas Haden Church or Rhys Ifans are actually credited in the movie and both Sandman and Lizard are shown digitally in their monster forms for the majority of their screentime, it's likely neither actor actually participated, meaning the brief shot of Rhys Ifans is likely also re-used from The Amazing Spider-Man. This technique is hardly new, and was seen as recently as Zack Snyder's Justice League, where several shots during Cyborg's Knightmare vision before Superman's resurrection were repurposed, including a shot of Henry Cavill's Superman in Man of Steel. The technique is far older than 2021, although it's usually more innocuous, such as, ironically, when Life reused Spider-Man 3 footage for a promo, although the final cut didn't actually include the scene.
It would have been exciting to see new footage of these actors reprising their roles, but with an already packed villain roster and COVID-19 production constraints, it's understandable why the movie went this route. In a way, it's also fitting for a movie so steeped in Spider-Man legacy to literally re-use footage from the previous Spider-Man franchises, making something that arose as a creative solution to a filmmaking constraint into a sort of fun Easter egg for fans.