Well, the idea to put ir-filter on webcam is to block parts of infra-red light-spectrum up from 700nm to avoid interference on the image sensor.
That's why technically we better have to say ir-
cutoff-filter.
So when working with ir-LEDs on the contrary we need this ir-band and not the part of visible light. That's why we use film or floppy disk for a ir-
pass-filter, that blocked visible light and let parts of ir-light through.
By the way as you can see in this
thread, floppy disk is a really poor filter that I can't recommend.
There's no way to avoid putting of ir-cutt-of-filter from webcams to make freetrack really works.
Multiple layers of colored films is a very effective way to create a ir-pass-filter (or visible light-cut-off-filter). Layers of red and blue spotlight-filter works great. Film from 3d glasses also.