A method of extracting a respiratory signal, comprising: capturing a series of image frames of at least a portion of a driver's chest, wherein capturing a series of image frames comprises using an image sensor to capture the series of image frames; identifying one or more objects on each captured image frame, wherein identifying one or more objects comprises: performing a binarization of each captured image frame with a threshold; applying a high-pass filter to each captured image frame in order to extract borders of the corresponding image frame; performing a dilation of each captured image frame such that the borders of the corresponding image frame are compacted; removing objects of the borders of each captured image frame; undoing the dilation of each captured image frame by smoothing the corresponding image frame with a same structural element; applying an opening to each captured image frame; extracting one or more features, respectively, of said one or more objects for each image frame; generating an object signal from the series of image frames, wherein generating an object signal from the series of image frames comprises generating an object signal from the respective extracted one or more features for each object and from the series of image frames; constructing the respiratory signal from the generated object signals. capturing a series of image frames of at least a portion of a driver's chest, wherein capturing a series of image frames comprises using an image sensor to capture the series of image frames; identifying one or more objects on each captured image frame, wherein identifying one or more objects comprises: performing a binarization of each captured image frame with a threshold; applying a high-pass filter to each captured image frame in order to extract borders of the corresponding image frame; performing a dilation of each captured image frame such that the borders of the corresponding image frame are compacted; removing objects of the borders of each captured image frame; undoing the dilation of each captured image frame by smoothing the corresponding image frame with a same structural element; applying an opening to each captured image frame; performing a binarization of each captured image frame with a threshold; applying a high-pass filter to each captured image frame in order to extract borders of the corresponding image frame; performing a dilation of each captured image frame such that the borders of the corresponding image frame are compacted; removing objects of the borders of each captured image frame; undoing the dilation of each captured image frame by smoothing the corresponding image frame with a same structural element; applying an opening to each captured image frame; extracting one or more features, respectively, of said one or more objects for each image frame; generating an object signal from the series of image frames, wherein generating an object signal from the series of image frames comprises generating an object signal from the respective extracted one or more features for each object and from the series of image frames; constructing the respiratory signal from the generated object signals. <EOS>