Windows 8

Windows 8 is an operating system released by Microsoft in 2012. TODO: add a little bit more information about 8

Wallpapers
Most of Windows 8's wallpapers were taken by Microsoft's design team, according to a UX designer who worked for Microsoft. It is the first Windows version since XP that does not credit the authors in the metadata. As a result, it is unknown who took what, with the exception of img4. The Flowers theme would later reappear in Windows 8.1 and Windows 10, while the Earth theme would be replaced by the Lines and colors theme in 8.1, and the Windows 10 theme in 10.

Lock Screen Wallpapers
Windows 8 came with a few built-in lock screen wallpapers, some of which came from Getty Images, while the others were created by Microsoft themselves, including graphic designer Marius Bauer. Most of these would reappear in 8.1.

At UX WEEK 2012, Jensen Harris, from the Windows design team, revealed that each of the lockscreen backgrounds was a reference to a design principle, as a sort of internal easter egg: img102 stood for "Authentically digital", img103 for "Fast and fluid", img104 for "Do more with less", and img 106 for "Pride in craftsmanship", while img101's beehive symbolizd the team's internal motto "Win as one".

User Account Pictures
Windows 8 become the first modern version of Windows without choosable sample account pictures since Windows XP. It has only 2 absolutely identical user account pictures used for default accounts and guest account respectively.

Both pictures have very high (comparing to previously used 128x128px) resolution of 448x448px. They were reused in Windows 8.1. Also it has .png-formatted versions of both of the pictures and resized versions of the user picture, probably used by Metro applications.

Picture Password
You can see this image in the Picture Password setup tutorial when setting it for the first time:

Setup background
The setup background called background_cli.bmp used by Windows 8 Setup. Since recovery menu was redone and now doesn't use any background, it can be seen only during Windows 8 installation. It can be found in the  folder inside of Windows 8 ISO. The background itself consists of simply, the default Windows 8 accent color. The same picture used in Windows 8.1 and 10.

Trivia

 * Windows 8 has a total of 13 wallpapers. It's 18 pictures less than included in Windows 7 (without regional images counted) and 1 picture less than included in Windows 8.1.