1. A method for determining the presence of volatile organic compounds (VOC) by detecting a drop in temperature at a leakage site, comprising: a computing device, wherein the computing device is configured to: detect moving regions in a current video image, wherein the detecting moving regions further comprises subtracting the current video image from an estimated background image; and determine that a detected moving regions has decreased wavelet energy by determining an average energy of the detected moving region in the current video image; determining an average energy of a corresponding region in an original image; and determining that the average energy difference is less than a threshold value.