Measuring kinematic fields using stereoscopic imaging is recurrent in the field of photomechanics, nevertheless, the heterogeneity of the refraction index of air along the optical path can become critical once such measurements are to be performed at relatively high temperatures. This study sheds more light on quantifying thermally induced errors in the case of the stereo-digital image correlation measurements (stereo-DIC) within the thermoforming temperatures range of thin thermoplastic sheets. A post-processing procedure is introduced to nullify thermally induced errors based on a series of isothermal rigid body displacements of the same speckled sample. Based on a segregation between bias and noise of errors, the experimental results provided statistical data which can be extrapolated to correct kinematic measurements conducted during the thermoforming process of thin thermoplastic sheets.