duplicate photos on my mac

First select the standard jpeg on your iPhone as the format to take:

As long as you're NOT using iCloud Photos you can use an app that will identify the potential duplicates, put them in an album or mark them with a keyword for easy retrieval and deletion by you. You don't want one that does the deletion itself for obvious reasons. 

I've run tests on the these two apps with the following results and found them to be safe to use:

PowerPhotos - $29.95  

PowerPhotos is the iPhoto Library Manager version for Photos and is very powerful. Although more expensive I would recommend it as it has more capabilities than the others like the capability to merge Photos libraries or copy photos, both original and edited versions, along with their metadata between libraries.

PhotoSweeper - $9.99 - Demo version available.

PhotoSweeper compares bitmaps and/or histograms so it can detect duplicate images even if they have different file sizes, file names, image sizes and capture dates.

Sounds like these photos were taken on an iPhone.

How are you transferring your photos from your iPhone to your Mac? (Examples would include iCloud Photos, My Photo Stream, and transfer using a Lightning-to-USB cable.)

In particular, are you trying to use more than one transfer/sync mechanism on the same photos? That can result in the specific kind of duplication you are seeing.