By using a variety of techniques that are beyond me, a group of enthusiasts have managed to find the seed for Minecraft's famous pack.png image. That seed is 3257840388504953787. However, simply loading the seed in a modern version of Minecraft isn't enough to generate the iconic scene; since world generation differs between versions, you'll need to load the seed in its original version: Alpha 1.2.2a.
Loading the seed
Since Minecraft versions prior to Beta 1.3 don't accept user input for the seed, it is only possible to load the pack.png seed through an NBT editor (such as NBTExplorer).
- Version: Alpha 1.2.2a
- Seed: 3257840388504953787
- Player position: (49.16, 64, 0.72)
- Player rotation: (-119.23, -8.297)
- FOV: 70
- In-game time: 34 seconds
- Window resolution: 1600x1116
- Crop position: (622, 284)
- Crop size: 512x512 (downscaled to 128x128 using SuperSampling)
Source: Tom Lacko
Alpha 1.2.2a uses the Alpha file format. In order to play the world in newer versions of Minecraft, it must be updated to a newer file format. First, the world must be loaded into a version which uses the Region file format (Beta 1.3 through 1.2). After that, it may be loaded into any version which uses the modern Anvil file format (1.2.1 and after).
EDIT 10/21/2021: the upcoming Minecraft 1.18 update will include a tool for blending biomes from older versions. When the update releases, I will be replacing my server's world with the original pack.png world.
EDIT 12/7/2021: the world file used on my server can be downloaded here. This world has been cut down and modified using Amulet so that the 1.18 world-blending technology works with it (biome set to forest, ocean level reduced by one).