Photographers can be gear-hungry people—upgrading equipment as better technology evolves. This often means that old cameras lie around unused. There is a small market for used equipment, but the price one can fetch for old technology isn't very high. As a result, many photographers convert old cameras to take infrared images.
Infrared light is not something that photographers want in a normal image. In fact, cameras have infrared filters placed in front of the sensor to prevent those wavelengths from being captured. When one converts a camera, the infrared filter is removed. The camera, in effect, becomes a "full spectrum" camera that can capture visible light as well as infrared light. By then putting a filter on the camera that allows only infrared light to be captured, it's possible to see the world in a different light.
The infrared light captured by a digital camera is near-infrared with wavelengths ranging from 550 to 900 nanometers whereas the thermal imaging that you might be familiar with deals with far-infrared in the range of 9,000 to 14,000 nanometers. Each type of imaging gives a different effect.
I purchased a converted, used Canon G16 from Kolari Vision so that I could get started with infrared photography. The camera comes with a set of filters that allow infrared light of a particular wavelength to pass through to the sensor. There is also a filter that allows all wavelengths and another that blocks infrared, essentially making the camera "normal."
The point-and-shoot Canon that I purchased is the easiest to start with because there are minimal technical issues compared to cameras with changeable lenses. The Kolari Vision website has excellent information on the technical issues and images of what each wavelength can produce.
Capturing an infrared image doesn't end with the capture. There are post processing techniques that one can use to get different color effects. Take a look at two images of the lookout point on my property. The first is what came out of the camera using a 590nm filter and setting the white balance by focusing on some green ferns. The second image was produced by swapping the data in one color channel to another. The first image looks apocalyptic while the second one looks like the cherry blossoms have opened on a beautiful day. (Those trees are fir, oak, or madrone.)
Infrared is best suited for landscapes in full sun. Normally photographers capture images in the early morning and around sunset, leaving the middle of the day for a rest break. Midday sun is too harsh for taking great photos. This is exactly when infrared shines. Because I often find myself out in the midday sun when I travel, I look forward to capturing the world in a different light.