I use a so called “808 car key micro camera”. These miniature camera's come so cheap (under 10 EUR), they are ideal for experimenting. You will beneeding a small Phillips screwdriver to dismantle it. If you go for the extra light version feeding from the flight battery, you will need an extra male and female plug compatible withe the flight battery and soldering equipment.
There is an abundance of information on the numerous variations on the market at Chuck Lohr’s non-commercial information site.
Check it out before purchasing one. I have a so called #3 and a #8 and confirm the #3 is better, as recommended on the site.
Do not expect top quality, but something suitable for fun. The motion blur is quite severe, in particular at lower light conditions. But for me, the main disadvantage is their narrow view angle. I have ordered a wide angle Jelly lens
to experiment on improving that, but it hasn’t arrived yet. So I will have to report on that later.
I stripped the camera from its disguise as a key fob, so it they weighs only about 10g. I covered it with some tape to avoid short circuiting the printed circuit board, but keeping free the Micro SD-Card slot and the mini USB port. The tape also keeps the actual camera in place, as it is attached to the printed circuit board with a flexible connection.
A folded Depron strip was taped to the camera to have it hang under the front motor.
If you want, you can power the camera on the flight battery, saving about 4g. In that case you will need an extra male and female battery plug to solder an extra connection in between the flight battery and the receiver (see the last 4 pictures). However I recommend not to charge the flight battery through the camera. The original battery seems to have some protecting/regulating circuit attached, while RC batteries count on the RC charger for that.