Origins of the Stop ' n ' Swop DK stuff?
 

These two images specifically.
https://i.imgur.com/rTDKVA5.png

The Donkey Kong painting in BK's house isn't out of place or special, as it's not strange to find references to Rare games in other Rare games. They probably removed it by the end of development purely I think just as an aesthetic decision—there's more to it than that though.

In later pre-builds of the game, that DK painting was moved to the one above the fireplace, where Bottles' painting is in the final game and where the secret puzzle minigame takes place. In the final game, Kazooie also calls Bottles "barrel boy" indicating that Donkey Kong was originally the one hosting this minigame. There's no indication that it was ever related to SNS, though.

The BK fridge in Donkey Kong's house would appear to be innocuous, but there's a way to glitch the game into showing you an unused cutscene. Presumably it would have shown the BK fridge opening up inside DK's house, after the player had just obtained the Ice Key inside Crystal Caves (There is unused text for ICE KEY in the DK 64 pause menu). You would then walk back to DK's house and ???????? special thing would happen.

I forget who said it or which interview it was, but one of the Rare staff members confirmed that Stop 'n' Swop was supposed to be a feature where collecting items in one game would trigger something special in other Rare games—not just from BK to Tooie. They said they only really worked on it for DK64 and BK, as the SNS idea was never fully fleshed out and the idea was scrapped. He said that they basically didn't even KNOW what they were going to use SNS for, or what would the mystery items would ACTUALLY do, but Dragon Kazooie was one of them.

Besides Banjo-Kazooie, DK64 was the only game where SNS was functional at once. In June 1999 Rare released Cold Swap Patent which explained Ice Key connection. There was blocked icy cave in Crystal Caves which was supposed to be unlocked with Ice Key from Banjo-Kazooie. The feature was cancelled between June 1999 and November 1999 when Nintendo forced Rare to remove it from the game. In released build we can find ashes of the feature - ICE KEY 1/1 in Totals and cutscene of Crystal Caves - DK House connection.

The very origin of SNS is releated to Spectrum era and the very end of Banjo-Kazooie development when Banjo Team got idea to connect SIX games and transfer "codes" between them.

I think the question here was where these images came from.

While digital photography has only relatively recently become mainstream, the late 20th century saw many small developments leading to its creation. The history of digital photography as we know it began in the 1950s. In 1951, the first digital signals were saved to magnetic tape. . . Yeah I got no idea sorry.

Where and when?

I remember that they were featured in RWP "DK64 Stop 'n' Swop Special" in 2003.

Yes, I was mostly requesting where the images came from. Like Magazines, official source, Rare themselves, so on.

I want a magazine and issue #, mostly so I can go and scan it with an industrial scanner.

Unfortunately, I don't know if anyone who would know this comes around anymore.

All I can find is this:

https://www.nintendo.co.jp/nom/9912/dk64/index.html

Since its an official Nintendo website, maybe it came from there?

And this being the 'largest' image of it I could find

https://pbs.twimg.com/media/D9ihRQXXsAAMmFY.jpg

Well that's one down! Hopefully we find the other. I'm sure it'll be a Japanese ad as well.

If the resolution is exactly the same for the BK one, I almost expect it to come from that Nintendo website as well. I snooped around a bit, and every image they used is the pretty much the same size. So likely there's not going to be a higher resolution available...unless another Nintendo leak happens :p.

https://www.youtube.com/watch?v=5MN4wS6u0ZU

Banjo-Kazooie "fridge" was located exactly at the same spot which is shown in Crystal Caves-DK House cutscene. My guess is that it was container for Ice Key transfered from Banjo-Kazooie.

I've never seen a larger image of the screenshot of the DK portrait in Banjo's house, but I feel like I've seen one that is slightly better quality than the one posted here. I also remember it being featured on an RWP page about BK beta content from at least 2003 when I joined the forums.

Since the speech bubbles are at a slight angle, my best guess is the source is a magazine or possibly even a photo of a TV from a convention demo. (Magazine or other print source seems more likely, mainly because the colors look like what could be produced by CMYK rather than RGB.)

Picture of Windmill level from Conker 64 (located in Mad Monster Mansion) was another cameo removed before release. As Jason said it was featured in RWP's Beta Banjo-Kazooie from 2003.