Life is unpredictable, and we can never be sure when we might be called upon to document events happening right in front of us. It may be the scene of a car accident, a crime in progress, suspicious activity or evidence gathering to protect ourselves - whatever the scenario, it's important, but often hard to react discreetly. But anyone with a smartphone can feasibly take discreet photographs or footage without being spotted. It just takes a bit of preparation.
First things first
If you want to be able to quickly take photographs without drawing attention to yourself, disable the flash and the shutter sound on your phone. The blinding flash of a smartphone is often what tips people off to the fact that they're being photographed. If not that, then it could always be the click. Depending on your phone, you may wish to alter the settings so you can quickly access your camera from the home screen without unlocking the handsets security PIN. iPhone users can do this by sliding up the camera icon that appears on the lock screen. Android users should look at their individual handsets instructions to enable this.
Disguise
There are plenty of ways to disguise your phone. You could use a novelty phone case, for example. Or you could modify your bag, a glasses case or anything sufficiently sized to house your phone. The next step is to learn how to operate it from the inside. A glasses cloth is often a good prop that can make you feel like you're cleaning your screen when you're taking pics.
Positioning
The trick to taking a discreet photograph is to behave like you're doing anything but taking a photograph. When texting, reading an article or browsing Twitter, we hold our phones in a position that makes it easy to view the screen. When we take photographs, we ignore this and hold the phone in a way that grants us the best angle for the shot. This is the dead giveaway. Practice positioning your body so that angling the shot looks natural.
For example, squatting down with your phone in a landscape position and then watching Youtube can be a good way to get a panorama of a room or outdoor scene. Laughing along with your headphones in will reinforce this ruse. You should also practice taking snaps without using the viewfinder or screen to frame your shot. Its tricky at first, but once you get used to angles, perspective, and general framing techniques, it starts to become second nature—practice, practice, practice.
Advanced spy camera techniques
Even if you've mastered all of the above techniques, you may still need to enhance your smartphones capabilities. For example, theres an iPhone app called Real Spy Camera which lets you set a fake screen background when you're filming. This prevents anyone behind you from seeing you filming or taking photographs. You'll need to work on your eyes-free technique for snapping pics with this.
What to do when a smartphone just won't cut the mustard
All of the above are great for snapping discreetly on the fly, but if you need robust, reliable evidence gathering, you're probably best served by investing in a real spy camera. Body-worn or hidden cameras give you reliable results and guarantee you won't be detected.