'A' No its not an actual photograph. Photographs are only good in the visible light spectrum (or close by) for example infrared and ultra violet.<br /><br />For example to measure radiation exposure, can be done with high speed film of ASA 800 or faster, incased in a light tight badge.<br /><br />You then wear it around the plant, later its carefully developed. If there is exposure the film will show up.<br /><br />Remember at airports you can't put high speed film through the machines. I have a few times travelled with ASA-1000 and insist its NOT xrayed, else its toast.<br /><br />Anyway back to your question. They measure radiation at different wavelengths. This data is then sent here where they can layer (as it has multiple instruments taking various readings) and you can combine them to end up with a 'virtual' picture.<br /><br />Think of it like your monitor works. You use 100% red + 100% blue + 100% green you get white. Also like component video, you have Y (being luminance) and U V being the colour broken up. Combine YUV you get a colour picture.<br /><br />Same principle here. Except its just basically readings that are all mapped together.