Most digital cameras have a filter on top of the sensor which filters out most IR. You can get an IR bandpass filter and put on the end of the lens, but this leaves you with a couple of different problems. First, since the IR filter is still on the sensor, very long exposure times are needed to get IR images. The other problem is you can't focus the camera once the IR filter is on the lens.
The other way is to have the camera's internal IR filter removed and replaced with an IR pass filter. This will block most visible light from the sensor and produce IR images. For the most part, the camera will work as before. It can be focused and exposed pretty much as a normal camera. The focus point will be slightly different, but as long as you use a middle to small aperture setting you won't have too many problems with focus. Some lenses include an IR focus point on the DOF scale.
Pure IR photographs appear as B&W, but some IR filters will allow some of the visible spectrum (reds, oranges, and/or yellows) to pass through. Post processing is used to convert the reds to blues and you get the "false color" IR images shown.
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