## 1 Introduction  
Photo mechanics and resistance strain measurements are generally recognised as the two most important and widely used methods in experimental mechanics. For the latter, researchers are convinced that temperature variation is a major factor that introduces a measurement error. Furthermore, a series of temperature compensation techniques represented by the bridge compensation technique have been used as standard error correction methods. All these techniques indicate that resistance strain measurement is a high-accuracy measurement method suitable for measurements involving long durations and complex environments in experimental mechanics. Recent studies show that temperature is a significant factor causing measurement errors in photo mechanics methods [1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16] as with resistance strain measurements. Previous studies have shown that temperature variations in camera systems introduce a thermal-induced error in the captured images. Since [PERSON] et al. [1] reported the influence of temperature on image acquisition, researchers have been considering temperature as a source of error. To date, a few efforts [2; 3; 4; 5; 6] have been made to reveal the image error induced by temperature variations in camera systems. [PERSON] et al. [2] used a fixed Pulnix TM6 CN camera to capture a series of static images with planar test patterns of circular targets during the camera warm-up. Furthermore, the targets in each image were located by a centroid subpixel location algorithm providing a precision equal to 1/50 of a pixel. Lastly, they found that the pixel drift of these targets increased with the duration of camera warm up, and the maximum pixel drift reached 1/5 of a pixel in both the \(x\) and \(y\) directions. [PERSON] [3] also analysed the impact of temperature variation after camera start up on image acquisition. A fixed planar test pattern consisting of 48 circular targets was captured by a rigidly fixed VRmagic-C3 camera during self-heating of the camera. The coordinates of the targets in these captured images were located, which showed a pixel drift from 1/10 to 2/5 of a pixel that depends on the position of the targets in the captured images. Undoubtedly, the previously mentioned pixel drifts are much larger than the well-known displacement resolution of 1/100 of a pixel in photo mechanics. Besides the previously mentioned pixel drift, the thermal-induced image distortion, which is directly associated with the strain measurement, was further investigated by researchers. [PERSON] et al. [4] performed experiments using an IMPERX digital camera, a planar test pattern with speckles, and the digital image correlation (DIC) method to investigate image distortion introduced by camera self-heating, and found an error magnitude of \(\sim\)10 \(\mu\epsilon^{\circ}\)C\({}^{-1}\), which is the same as that observed in resistance strain measurements. [PERSON] et al. [5] investigated the effect of camera temperature variations on image acquisition using stereo-DIC with a stereo-DIC system consisting of two industrial cameras (GRAS-50S5M-C, Point Grey Research, Inc, a company located in Richmond, Canada.) and found a thermal-induced distortion of approximately 30-50 \(\mu\epsilon^{\circ}\)C\({}^{-1}\). Note that, after a camera is switched on, generally, temperature changes of \(\sim\)10 \({}^{\circ}\)C can occur and can be even higher, depending on the environmental temperature. Thus, the induced image distortion can reach hundreds or even thousands of micro-strains, which is considerable when compared to the strain resolution of approximately 100 \(\mu\epsilon\) in photo mechanics methods. To sum up, the temperature variation in camera systems will introduce significant image errors compared to the displacement and/or strain measurement resolution of photo mechanics methods in terms of pixel drift or image distortion.