The idea came up, when I wanted to develop a device to take pictures at a party without blinding everybody with a strong flash.
So what do you need:
Some IR-LEDs, the stronger the better (20-60 pieces)
a power transistor (i.e. BD649)
some capacitors (1000uF or more)
one resistor (50Ohm)
an old mouse button
and some breadboard
To use it, you need of course an IR-sensitive camera. You can build these by yourself or get someone to convert it for you. Look at these guys here: www.lifepixel.com
My other instructable is about how to make a Nikon 4300 IR sensitive. Look here!
Step 1: The principle
Some LEDs are suitable for this, others not. You should try to find out before ordering a large quantity. In the data sheets this value is called peak forward current or surge current. It should at least be something around 100mA or more, while the normal forward current is 20mA for most LEDs.
In the picture you see the data for some diodes called SFH4650 with a normal current of 100mA and a surge current of 1A!!! The higher the peak current is, the longer has to be the time between two events. Say you flash 1A for 10ms then you should wait at least another 90ms before flashing again. But normally this is not a problem when triggering by hand.
Also check the wavelength of the IR-LEDs. Anything above 780nm is enough to be out of the visible range but in the center of the sensitivity of a IR-Camera. 850nm is nearly perfect, those with 920nm are too dim for the camera to see.