Image recording equipment can now be used by anybody, and the low costs of these devices have contributed to their popularity and universal availability. Analytical methods based on the use of this type of equipment can help in the control of pollution in remote regions that lack access to laboratories, as well as in developing countries, where the costs of acquiring and maintaining commercial instrumentation hinders the implementation of environmental monitoring. The present work therefore describes the application of digital processing of images acquired in the visible region, for the determination of NO2 present in the ambient atmosphere. This approach is shown to be a highly effective alternative for the in situ determination of the compound, and could assist in the monitoring of atmospheric pollutants in different environments and locations worldwide.