https://www.doomworld.com/vb/doom-general/85756-found-doom-sky-source-files/
Here is some additional info and pictures that I've found.
By
imx-doomer:
Remember Blackmantis, the incredible Doom fan who was (and still is) hunting the source for each one of the game assets and found out about the toy used for the BFG? Well, it turns out he found the source for some of the skies used in DOOM and Doom 2: Hell on Earth.
As some of you may know, Episode 1, Knee-Deep in the Dead, uses a gray sky with mountains, a sky that has become iconic in retro gaming culture, partially because, as many other assets found in DOOM, it was sourced from a real picture taken in Yangshuo, a beautiful city in China with some gorgeous mountains. Said picture was included in a CD called
“Media Clips”, released by Aris Entertainment around 1992 (that would explain why it was used in DOOM, since the game was released in late 93). The exact picture in question was taken by Tom Atwood, in Yangshuo Cavern, near Guilin, China
Of course, almost every DOOM fan knows about this, so the reason why I’m doing this post is because the fun doesn’t stop here.
Blackmantis found out about this sky right here. When you see it…
You don’t? Okay, let me help you a little bit.
Isn’t that…yes, the Doom 2 sky was sourced from this picture! It seems that they took a fragment of this picture and they made it tile horizontally, to avoid making it look ugly in-game. Trust me, a sky texture that doesn’t tile is not always a good thing to look at in Doom.
Now let’s take a look at this picture from the Columbia shuttle taking off.
Nothing? Well, here it goes.
Okay, so this part right here is interesting.
Doom 2’s city sky is a combination of this picture, and the unused Doom 2 art made by Julie Bell, part of the destroyed buildings, to be more specific.
All of this was posted in this Doomworld thread
right here. Another Doomworld user called Jaws In Space discovered that the canyons in the sky graphic used for Episode 3: Inferno were sourced from a picture taken inside the Carlsbad Cavern, located in New Mexico. Naturally a fragment of that picture was cropped and edited to match the hellish tone.
At the same time, Blackmantis found the picture used for the background in the Hell sky, which is…
This one! If you don’t see it, then here’s the hellish sky texture overlapped with the picture itself.
Now you might wonder,
is there a place where I can download that CD with all those old pics?The answer is yes, and it actually has been uploaded in The Internet Archive inside their Shareware CD collection! You can grab a special edition of the MediaClip set
right here! (220MB)