Information found in another forum-
The Photos app operates using a library, like iTunes. When it imports photos it's not immediately obvious where they've been stored. In fact they're buried inside the ‘Photos’ library; to find them you do the following.........
*Just a warning on the following - don't disturb the folder or file structures in the Photos library - if you want to move your image files elsewhere I suggest that you copy them from the library and paste them where you want them (see step 6 below)
1. Open Finder and navigate to the Pictures folder on your hard drive.
2. Locate your Photos library folder - it has an icon like the Photos app and the file extension .photoslibrary.
3. Right click on the Photos library folder and select 'Show Package Contents'
4. Now you will see a whole host of folders, including one called ‘Masters’ which is where your image files are stored by the Photos app
5. You'll find as you drill down into the folder structure that things are arranged by year, then months in subfolders then days in a further subfolder then finally the folders containing images. These latter folders are labelled as the precise time of the import e.g. 20151212-092245 is my latest one.
6. If you wish to recover your image files and store them in another location then select the files, copy them and finally paste in the new location rather than moving the originals from the library.
7. If ultimately you decide not to use the Photos app and want to delete the copy of your images stored in the ‘Photos’ library then always delete your images from within the app itself and not directly from Finder.
Import the 'copied' files into Lightroom from the 'new location'.