This very solid pouch will allow you to take pictures & video in a very discreet way.
Hidden in plain sight, nobody will pay attention, unless the "people who know".
The "stealth smartphone pouch" and the next to come "sport smartphone pouch" are very easy to build.
List of material;
One plastic pouch, for instance ID card holder, diy laminate pouch etc...
A metal clotheshanger
1 meter of thin nylon wire
1 eyeglass lanyard paracord (but you can make your own)

Step 1: Pouch

Find a pouch to fit your smartphone ( iPhone, Android or Blackberry)
Important; one side of the pouch needs to be clear, transparant, so you can see the screen.

Step 2: Wire

I use wire from a clotheshanger.
Just unbend it and make a frame around the pouch, leaving 5mm on the sides.

Step 3: Tape

Tape the frame to the pouch with transparant tape, it is much easier to saw.

Step 4: Needlework

It is easier to use a thick needle.
Any type of solid wire will do.

Step 5: Eyeglass Lanyard Paracord

Buy an eyeglass lanyard paracord.
Another option is to make your own.
Bend the frame wire with a solid tweezer, into a hook.
Attach the eyeglass lanyard paracord to the hook.