Duplicate Annihilator Process order removed

Here's what they say:

Duplicate Annihilator...keep[s] the photo with the highest resolution/largest file size as the original.

Which is not necessarily the same as your requirement

the one that has been edited most recently

It could be but there is no way to be sure. Simply, they're keeping the highest quality version, your requirement takes no account of quality at all.

If you have a lot of photos to sweep, you might try a different tool - Photo Sweeper. But it is not a free app.

Photo Sweeper gives you more control over the rules, which photos to mark for deletion

You can change the priorities of the rules to favour the newer photos by setting the preferences:

This app is safe to use. It just marks the photos for manual deletion or moves them to iPhoto's Trash and does not modify the library directly.

What you can do is create a smart album with the criteria Photo is Edited.

This will give you access to all edited photo from where you can batch give them a rating, keyword or description. I used a rating of 5 stars in my test.

When DA has scanned and added "dup" to the description of all of the found duplicates

you can create two more smart albums with the criteria:

Smart Album 1

Descriptions contains dup

This will show all photos that DA found.

Smart Album 2 - duplicated photos.

Descriptions contains dup

Rating is 5 stars

This will show all photos that DA identified as a a duplicate and you gave a 5 start rating to.

Now a 3rd Smart Album with the criteria:

will give you those photos that were found to be duplicates but were edited photos. To remove them from the Album #2 change the rating of those photos. They will drop out of Smart Album 2.

You'll have to find the other copy of those edited photos and manually delete them.

Now you can select the photos in Smart Album #2 and use the Command+Options+Delete key combination to move them to the iPhoto Trash bin. Empty the trash bin and they're gone from the library. Don't forget to empty the Trash bin in the Dock to remove them from the hard drive.