This document describes a system for detecting driver drowsiness based on yawning detection using video images of the driver's face. The system first detects the face and extracts features of the eyes to determine eye state. It then analyzes mouth movements to detect yawning. Yawning detection is performed using k-means clustering to group mouth images by similarity and identify yawning behavior. The system was tested on a dataset of video recordings and able to accurately detect yawning 93.18% of the time to identify signs of driver fatigue. This type of non-intrusive drowsiness monitoring system could help reduce accidents caused by tired driving.