Junk Yard · What gets captured
Why didn't my screenshot appear in the Junk Yard?
Short answer: macOS saves normal screenshots as files, which the Junk Yard doesn't see. Add Control (⌃⇧⌘4 or ⌃⇧⌘3) to copy the screenshot to the clipboard, and it lands as an image scrap.
Because it was saved as a file rather than copied. A normal macOS screenshot (⇧⌘3 or ⇧⌘4) lands on your desktop as a file, and the Junk Yard only catches what goes onto the clipboard.
To send a screenshot straight to the Junk Yard, add Control to the shortcut — ⌃⇧⌘3 or ⌃⇧⌘4 — which copies it to the clipboard instead. Or copy the saved screenshot file in Finder (⌘C) to add it as a file scrap. Learn more about screenshot shortcuts on Apple's support site.