Photos (OS X Yosemite / El Capitan) – show original in Finder?

Solution 1:

Photos expects you to export unmodified originals as copies, to preserve the integrity of the internal file management and for collection protection in the same way a database works – it's central to keeping the iCloud storage of your photo collection synced, stable, and functional.

Once you have exported a photo, you can then use mdls and mdfind to see what the "copy" looks like and where the original was stored.

In my case, they are all in ~/Pictures/Photos Library.photoslibrary/Masters/2015/04/08 and such stored by year, month and date for my US locale computer. You'll only have to do this exercise a few times to nail down the internal storage for each time Apple chooses to change it going forward.

Solution 2:

This is another approach:

1. Open Photos and go to the photo you want.
2. Right mouse click and choose Get info. Here you can copy the photo's file name
3. Click on the Magnifying glass icon on the top right corner of the screen. Paste the photo file name there.
4. Maybe you have to wait some seconds, then Double click "Show All in Finder" in the search dialog.