Can I delete iPhoto app?

If you have no longer any Mac compatible with iPhoto, delete the app - Photos does not need it. Otherwise save it on an external volume, just in case you need to open old iPhoto Libraries, to compare the metadata of your photos in Photos and iPhoto. You may mot be able to get iPhoto back, if you delete it. If your Mac is not able to run iPhoto any longer, the app icon will be crossed out, like below.

If you didn't have any problem after the conversion of your iPhoto library to the new Photos library,

a few MacOS upgrades ago,

then you can simply delete this application.

Photos doesn't use iPhoto, you could even use iPhoto and Photos on the same Mac.

This was the case for many users who had problem with the conversion procedure.

Even if the conversion has been without problems, the result will not have been perfect. You may want to look up missing metadata after the migration to Photos and recreate smart albums and projects and adjustments and named faces.

Photos can only migrate the metadata that can directly be recreated in Photos. Most smart albums will be missing, because the rules could not be recreated. Some dates and times may be wrong, you may need to recreate the adjustments, because you cannot edit the adjusted photos further without having to discard the adjustments. There may be many reasons to look at the original iPhoto Libraries again, while you still can.

You can just delete it.

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