A gas concentration-length quantification method, including: acquiring a first image including a gas plume with a camera; identifying and segmenting pixels corresponding to the gas plume in the first image; generating a background image corresponding to the first image using an image inpainting algorithm with the first image and positional information of the segmented pixels corresponding to the gas plume as inputs; calculating a gas concentration-length for each pixel corresponding to the gas plume in the first image, based on the first image and the background image data; and triggering an alert when the gas concentration-length for at least one pixel exceeds a threshold level.