I was just curious about why Popclip isn’t invoked when I select an image. Thanks.
PopClip only appears when you select text. This is intentional by design.
If you select some text that has a photo embedded in it (e.g. rich text in TextEdit) then PopClip will appear.
If you select a photo file in Finder, or in an app like Photos, PopClip won’t appear.
(As a rule of thumb, if the mouse pointer changes to an “I-beam” shape when making the selection then it’s text, and PopClip should appear. If it stays as an arrow or changes to a different shape like a crosshair, it’s probably not text, and PopClip won’t appear.)