
If your library is large, and you want to free up storage space on your Mac, turn on iCloud Photo Library and use Optimize Mac Storage, or move your library to an external. Your Photos library holds all your photos, albums, slideshows, and print projects. Put the other machine into target disk mode and connect it directly to the merging machine.
Copy the library from the other machine onto an external hard drive, then connect that hard drive to the merging machine.This is the recommended approach, assuming you have enough free space. Rather than using the library directly over the network, you can instead first copy it to the merging machine's hard drive, and then perform the merge using the copy of the library instead.
Instructions for doing this can be found here.
Set up one machine to access the other machine's library directly over the network. This can be done a few different ways, including: If you have iPhoto libraries on two separate computers and would like to merge them together into one library, the first thing you need to do is choose which machine you'd like to use to perform the merge (we'll call this the 'merging machine'), and make both libraries accessible from that machine. Hello, Photo is not at all my photography main app but it comes handy at importing off of the iPhone, I just figured it out that on my backup MacBookAir I have two Photo libraries and was trying to find out how to merge them in a single one as to save space (there probably are doubles) and to. One common thing I'm asked about as an Mac consultant is how to manage iPhoto libraries that have gotten out of hand – thousands of photos, lots of duplicate items, and sometimes multiple.