Yeah, I modified an old CVS disposable digital camera to do this once. Those filters only block near IR (as mentioned in the article), basically light just outside our vision spectrum. You can use infrared LED's and a camera thus modified to make a cheap night vision camera (This is, I believe, how the night mode on old sony cameras would work).
Measuring heat, however, requires far IR, which won't be picked up by removing the filter.
Exactly. Near and far IR are different beasts. Not only are the sensors different, but you need to make the lenses out of different material (or use mirrors).
Measuring heat, however, requires far IR, which won't be picked up by removing the filter.