For individuals trying to just stop Photos.app from launching on their own computer just follow this:
https://captureintegration.com/quick-tip-stop-yosemites-photos-from-opening/
I am going to reply once more. My environment is a network environment with about 20 iMacs connected to one MacPro with Server all MacOS 10.9+
I was able to finally figure out how to get AutoImporter.app or another app of my choice to open instead of Photos.app but since we are on a network using opendirectory I was able to use Workgroup Manager. I imagine you could do this same thing but instead of opening the network directory you could open the local directory and add this preference for local users group instead. I had to have the following software Plist Edit Pro, Workgroup Manager, RC Default App in order to accomplish this.
Within the ByHost directory is a preference file that gets generated: com.apple.ImageCapture2.A3606F44-XXXX-XXXX-XXXX-XXXXXXXX.plist (I x'd out my machine ID)
The above file can contain two different types of entries 1 type is specific to an SD card or camera, the other type is generic to all devices. RC Default creates the entry that will work on all devices. Photos and Image Capture will only allow you do setup your system per SD card which is terrible because that means that every SD card you stick in or even after you format an SD card you have to set it up again to not automatically launch Photos.app
Another consideration of the preference file above is that since it has that long machine ID on the end you would have to rename it with your machine ID when you copied it into your own ByHosts folder because it will not work otherwise. Thats why I mentioned Workgroup Manager, it has the option to apply a ByHosts preference file like the one above to an entire group and have it apply to anyone who logs in.
Example of the key inside the preference file that is per device:
F615FDFB-8079-3BE8-ADE9-4A312E1AB04E
ICADeviceTypeKey String ICADeviceTypeCamera
autolaunchApplicationPath String /System/Library/Image Capture/Support/Application/AutoImporter.app
Example of the key inside the preference file that will affect every sd card or camera plugged in:
HotPlugActionPath String /System/Library/Image Capture/Support/Application/AutoImporter.app
As long as you do not uncheck the box under the import tab of Photos.app for each device and just go into RC Default App and just switch the Camera entry to a different app the HotPlugActionPath key above gets generated.
Now my issue is that I have setup an applescript to launch which warns my users that their pictures will be imported and then launches AutoImporter.app but the problem is that if I just manually launch it for some reason it will not Import the photos.
Can someone else try this please? If you have the Camera app in RC Default App set to none and so when you insert an SD card it does nothing and then you manually launch AutoImporter.app does it download your photos? It appears that for some reason it has to be triggered by the HotPlugActionPath key or something to work?