In this study, we present a particular technique that was developed to assess and quantify mental stress states using a low-cost webcam. The input signals are recorded on human faces and image and signal processing algorithms, bases on the continuous wavelet transform, were developed to remove trends and noise generated by involuntary motion artifacts. An interactive version of the Stroop color word test was employed to induce stress. The electrodermal activity was recorded in parallel using a contact skin conductance sensor. This particular signal has extensively been used in psychophysiological experiments and is well-correlated with arousal responses. A set of basic parameters was computed from the webcam pulse rate variability, forming a stress curve that was compared to the skin conductance level. The results offer further support for the applicability of stress detection by non-contact and low-cost means, providing an alternative to conventional contact techniques.