Why does Photos show pictures that I have not yet imported, and are still on my hard drive?

Before importing pictures into Photos I use Image Capture to download the pictures from my phone into a folder in my hardrive. Then I change the file names working with Finder or sometimes with Automator. When I'm done with this, I open Photos and import the pictures from my hardrive (a temp folder in the Pictures folder).

What I notice is that Photos already shows the pictures that I am about to import, with the original name (e.g., IMG0567.jpg".

Are the pictures therefore already in my Photos Library? When I import the pictures with the edited filenames, will I end up with duplicates? Thanks to anyone who can shed some light onto this...