How to duplicate-check between iPhoto Library and Photos Library *and* move non-duplicates from iPhoto -> Photos? I'm working on merging a 11000+ image iPhoto Library with a Photos Library - with the purpose of pushing it to iCloud Photos.

I'm not exactly sure how to proceed. I know that my friend has new images on the Photos Library that aren't on the iPhoto Library - so I can't just ditch the Photos Library and do a one-way import.

Does anyone know which app would currently allow for this? I mean, I just used iPhoto Library Manager to merge three iPhoto Libraries on 3 separate machines into one, and now it seems there's only one hurdle (mash together iPhoto &amp; Photos Libraries) before I can deliver the images to her iCloud Photos.

Is there anything you could offer as advice for accomplishing this, as it has been a very long task (took something like 6 hours to combine three iPhoto Libraries which were all on 3 different computers, to boot :) )

I'm thinking a few approaches are possible, but who here would know which one to take?

1- Convert iPhoto Library to Photos Library and find an app that can merge + de-duplicate two Photos Libraries.

2- Find an app that can merge + de-duplicate an iPhoto Library and a Photos Library into one Photos Library.

Also, once this is done, is it just a breeze to push it to iCloud Photos, or should I somehow prepare further?
Perhaps a little bit late for esaruoho's friend but might be useful for someone else.

FatCatSoftware, who created the iPhoto Library Manager that esaruoho linked above, have created a similar application for managing Photos.app libraries called PowerPhotos.

For this situation I would go with option 1. 


Convert the iPhoto Library to a Photos.app library.
Combine the two Photos.app libraries into one by using PowerPhotos.
Run a duplicate image check using PowerPhotos in order to make sure there are no duplicates.
Upload images to iCloud.