Keep all my photos in the Apple Photos App on my iMac

Is there a way to keep all my photos in the Apple Photos App on my computer (iMac or Macbook Pro) even when I delete them from my iPhone, iCloud and/or my iPad. I realize that iCloud is a syncing Cloud, however, there should be a way for me to change a setting so that the Photos app on my computer will keep all of my photos on my computer even when I delete them from my other devices. My computer is a bit different then an iDevice. These iDevices are mobile and colectors of information and my computer is a storage device for keeping all my documents safe and secure. I do realize that I can copy all of my photos out of Photos and into a folder, however, then I have duplicates. Not a valid solution. SO, is there a way to keep photos in the Photos app when they are deleted from my iDevices. If not, there should be a setting for that.

If there isn't and any of you would like to see that feature, please write to Apple and give them feedback at www.apple.com/feedback . Thank you for any suggestions and or for writing to make this a feature in Photos!