In this video, the author is showing how he converted a cheap camera into a infrared thermal camera.
Explaination: Every camera sensor has ability to see infrared i.e. thermal part of the light, but the infrared’s blocking filter inside a digital camera protects the CCD sensor from burning with high energy infrared light such as sunlight .
Now , if we remove the blocking infrared filter the camera can will be able to see infrared part of the spectrum of light.
Courtesy: Kedar Nimbalkar