Most digital cameras are designed with filters that allow the sensor to record visible wavelengths of light - but excludes infrared (IR) light. The reason for this: allowing the sensor to receive IR light typically results in unwanted color casts or blurry edges in an image - not so wonderful.
Something wonderful does happen though when that IR blocking filter is removed, and another filter is added to block visible light. The camera sensor registers the infrared light, and the camera imaging logic interprets that as "more infrared = lighter areas in the image". In my workflow, the resultant image initially has red/orange/purple hues, and mapping that to a black and white or sepia tonal scale can yield pleasing results. Here are some examples.
The image below shows an old railroad track bed that has been repurposed and resurfaced to create a recreational path. The plants register in lighter shades (reflecting a lot of IR light) while the rock walls register in darker shades.
