All this resource pack does is inserts the retro pack.png file in as a 2x2 painting, for those feeling a bit nostalgic for the old days. I changed the frame of the painting to match stage's because I thought the aqua frame looked a bit weird without the rest of skull_and_roses.
Please note that there are different files depending on whether you're playing before or after 1.14 - this is due to how paintings are saved internally. Make sure you have the right version of the resource pack selected before you download.
The down-scaled version of pack.png is available here for anyone that, for some reason, would need it.
If you are, at all, interested by the image and its origin, then check out the project being led by SalC1 to find its world seed here.
Edit: Seed found! Thanks to everyone who lent their processing power towards seed scavenging.