The wallpaper behind the windows is always a very important part of a product branding. Apple is particularly good at choosing the right image. Here is a gallery of default wallpapers of every Mac OS X version.
Mac OS X 10.0 Cheetah, 10.1 Puma
Gentle arches in the well-known blue.
Mac OS X 10.2 Jaguar
A new one in the same style: instead of abstract arches we got glowing lines.
Mac OS X 10.3 Panther
The same blue again.
Mac OS X 10.4 Tiger
It is very interesting, that Apple took the time to refine the details of the wallpaper. It is almost the same as Panther’s, but not exactly.
Mac OS X 10.5 Leopard
Leopard brought a brand new direction: space. Until Mavericks Apple shipped every OS X with space themed wallpapers.
Mac OS X 10.6 Snow Leopard
Just as Snow Leopard was a refined version of Leopard, it’s wallpaper was a refined version too.
Mac OS X 10.7 Lion
This is the only wallpaper, which is missing from the current OS X Yosemite installation. The reason might be the poor image quality despite the large size.
OS X 10.8 Mountain Lion
Another refined iteration. This galaxy is less colorful and much higher in quality.
OS X 10.9 Mavericks
When Apple ran out of cat names, switched to places. Mavericks is a famous surf place not too far from Apple’s HQ. The beautiful colors of this wave tell you the story.
OS X 10.10 Yosemite
After the beach we went to the Yosemite National Park. This release includes a bunch of high quality images from the famous rocks of the park. The selected default wallpaper was a perfect demonstration for the new transparent interface of the operating system.
OS X 10.11 El Capitan
El Capitan is the name of one of the the most beautiful rocks in the Yosemite National Park. The resolution increased to 5120×3200, the resolution of the 5K iMac.
macOS 10.12 Sierra
The new wallpaper is about a mountain too.
macOS 10.13 High Sierra
Of course High Sierra, the highest part of the mountain is also a mountain image.
Pro tip: 512pixels web site has some of this wallpapers remastered in glorious 5K resolution.
macOS 10.14 Mojave
The wallpaper is actually a HEIC file with multiple images for each part of the day, which can change dynamically. You can find all the images extracted here: https://github.com/xtai/mojave-dynamic-heic
macOS 10.15 Catalina
HEIC file again. The one shown above is only one of the series. You can find the full original file here: http://osxdaily.com/2019/06/06/get-macos-catalina-default-wallpapers/