Following are the steps to Move Photos and Videos from Google Drive to iPhoto on Mac:
1. Go to https://drive.google.com/ & sign in to your account.
2.Download "Google Drive Desktop Application" on your Mac from the Apple App store & launch it.
3.Open "iPhoto" on Mac.
4.Click "File" tab.
5.Select "Import to Library..." option.
6.A "Finder Window" opens up.
7.Locate the Google Drive folder containing the photos and videos which you want to import.
8.You can select the photos, videos or an entire folder. Drag and drop them into iPhoto viewing area.
9.This is how you can move photos and videos from Google Drive to iPhoto on Mac.
Source : https://www.picbackman.com/tips-tricks/how-to-move-photos-and-videos-from-google-drive-to-iphoto-on-mac/
Useful link : Google Technical Support