IR photographs have a strange, other worldly appearance. That’s because the range of light wavelengths used to form the image is not the same as the range our eyes see (although some animals apparently see into the infrared). The wavelength range for the human eye is from about 300 nanometers (nm) to 700 nm (or 3000 Angstroms to 7000 Angstroms). Most digital camera sensors can record wavelengths outside this range, but light in the near near infrared (700 nm – 900 nm) focuses at a different point from visible light. So, digital cameras, in order to avoid “fuzzy” focus, include a blocking filter which removes the near near infrared light.
There are companies (e.g. http://www.lifepixel.com/) which will carefully remove the infrared blocking filter from your camera and replace it with a filter designed not only to pass some or all near near infrared light but also to protect the sensor surface from dust and scratches. Now you’ll be able to take infrared photos, although adjustment to proper focus will be necessary, and your camera will no longer be able to take regular visible light photos without further processing of the image. In short, unless you have an unused camera lying around which you could get converted to infrared, you’re better off purchasing a camera designed to take infrared photos.
Here are some wonderful examples of IR photographs, by Doerte Pavlik, taken with a full spectrum camera. The images were captured in Death Valley, Monument Valley, the Grand Canyon and other places in the US Southwest.