Continuous monitoring of the respiratory rate is necessary, particularly for patients stationed in the hospital's wards, to assure their physical conditions are medically controlled. We tested the developed webcam-based contactless respiratory rate monitoring system on twenty healthy volunteer human subjects (age 20-25 years old) who provided informed consent to participate in the research. Subjects are asked to breathe with the breath rate following the guiding flash lamps emitted from mobile phones at specific rates. Results show that the developed system is capable of measuring respiratory rate with an average error of 0-2% and with an average coefficient of variance (COV) of 0-5% among all subjects tested and for all ranges of respiratory rates investigated. These results are quite promising for further use of this system as an accurate and precise continuous respiratory rate monitoring system in clinical settings.