QuickLook was added back in 2007, to OS X 10.5 Leopard: https://en.wikipedia.org/wiki/Quick_Look
cached images go in /var on the boot drive
Something so commonly-known that even I, not exactly a Darwin kernel dev, knew that. Another comment called TFA "blog spam", and I can't argue strongly that they're wrong.
too bad the original blog (if it is the original) is undated.
side-bar: how do you know this? is the information about the file structure of linux available somewhere? I've only ever run into this type of thing circumstantially.
However, it's become a pain lately anyway in that it doesn't work for images [maybe over a certain size?] stored in iCloud (unless it's already downloaded) which includes the desktop folder and therefore screenshots (because letting you store screnshots anywhere else by default would be logical and we can't have that). Nor does it show anything to indicate this, it just appears to randomly work or not work. I wish they'd send a lower res version for previews, or something, as more and more stuff moves to the cloud.
I haven't looked to see whether there's a keyboard shortcut to jump to the next image. It's not up/down arrow.
defaults write com.apple.screencapture location ~/Screenshots
killall SystemUIServer