Do you need the Photos.app available for people to use, or is this a deployment machine where you can "disable" that app? If you don't need the app for anything here is what I did in my photo lab where students are using Adobe Lightroom and Photoshop.
Restart and hold Command+R to go into recovery mode. Open "Terminal", found in the "Utilities menu" and use the commands
$ csrutil disable; reboot
to disable SIP.
Once the computer restarts, go into the Applications folder and "Get Info" on the Photos.app. Twirl down the permissions section and set "Everyone" to "No Access". This will keep the app installed, but nobody can open it.
Restart and hold Command+R to go into recovery mode. Open "Terminal", found in the "Utilities menu" and use the commands
$ csrutil enable; reboot
This will reenable SIP. Now when you plug in your iPad cart (or anything else that has photo's on it) the Photos.app will not start (well it starts, then stops immediately).
Let me know if this works!
**** Guess I should have read the whole thread. Seems this answer has already been given.