How can I import all my photos from old iPhoto on an external disk to my new Photos
How can I import all my photos from old iPhoto on an external disk to my new Photos, 0S 10.13.2
iMac (24-inch Early 2008), Mac OS X (10.6.8)
How can I import all my photos from old iPhoto on an external disk to my new Photos, 0S 10.13.2
iMac (24-inch Early 2008), Mac OS X (10.6.8)
Make sure, the external drive is correctly formatted. The file system format should be MacOS Extended (Journaled) or APFS. The drive must not used by Time Machine.
Then drag the iPhoto Library onto the Photos icon in the Dock. Photos should now create a new Photos Library from the iPhoto Library.
If the iPhoto Library is from a very old version - iPhoto 7.1.2 or older, you need first to run the iPhoto Library upgrader to prepare the library. iPhoto '11: About the Library Upgrader
The procedure above will give you a second Photos Library and you can switch between your current library and the migrated version of the iPhoto Library. Photos cannot import libraries directly. You will have to export the photos from the second library with Photos and import them into your current Photos Library, or use iCloud, or get yourself PowerPhotos.
See: Notes on Merging Photos Libraries | Apple Support Communities
How can I import all my photos from old iPhoto on an external disk to my new Photos