When I search for photos in finder I can see just Photo Booth's photos:
But I have a lof of pictures in Photos app, why can't I see them?
Update
The option "use as system photo library" (in Italian: "usa come libreria foto di sistema") is disabled.
Best Answer
It seems like you might need to open the Photos app, and within Preferences choose "Use as System Photo Library"...
Source: https://discussions.apple.com/message/28138885#28138885
However if this doesn't work it would suggest something on your Mac isn't setup right and you should try backing up your data and reinstalling by following these instructions.