Can I use a cell phone camera as a spy camera?
In case cellphones are allowed at the location at all and you can disguise your smartphone so that not to arouse suspicions while making it overseeing the scene, it is possible. Even remotely: for Android, you can use AirDroid app for remote control and IP Webcam as an actual camera app for remote surveillance.
For example, you turn your phone into flight mode while leaving Wi-Fi on, shut down all messaging apps and notifications, carry your phone in your front suit pocket or something similar with a camera looking outside, and that's it.
Also it is quite possible to conceal a phone (powered and connected, in silent mode with notifications shut down) over an Armstrong-type ceiling.
At this stage of the game, it doesn't really matter whether or not he's cheating or she is cheating. You suspect that he/she is. Whether you're right or wrong about that, you clearly don't trust him/ her .So the lack of evidence proves nothing to you.Then, you'll conclude that he's even craftier than you thought, and he's covering up too well to get caught.....
It's absolutely possible to activate the camera and access it remotely.
Usually someone would upload a malware to your phone in order to access it, however access is given to everything not just a camera.
You can detect it though, e.g. battery drainage. On iPhone you can easily detect that camera is heavy on your battery, though you use it few times per week.
But everything is possible with right tools, desire to make it happen and a knowledge.
Recovering the information you need is really not a big deal, but why do you really need such data? its illegal to search through peoples phones and devices; private life in general, but still we have to be sure of what we are getting ourselves into these days, in this life one thing i know is that Karma exists and it could clap back anything, can we not be cheats and be loyal and honest with eachother, life is short and you only live once; #YOLO. The latter of the case should always be reckonedwith, of which it would be known eventually what would be the data at hand afterwards. Definitely!!!