We devised a way to measure blood glucose non-invasively by applying Derivative Spectroscopy to the images we recorded with a smartphone camera. Based on two years of testing several methodologies to quantify blood glucose levels, we used principles of the Beer-Lambert Law to correlate the ratio of two wavelengths to mg/dL blood-glucose values. To non-invasively calculate the intensities of the two wavelengths that had been transmitted through a volume of a subject's blood, we passed a single wavelength through a subject's finger, once placed on a smartphone camera that acted as a photo-detector. We then discovered a near-linear correlation between the ratio of these two wavelengths and blood-glucose values. Future work entails tailoring the methodology to account for the influences abnormal properties of the blood have on transmitted wavelength values, and facilitating dynamic re-calibration for these abnormalities.