Whenever any engineering system comprising of an internally heated channel/tube is exposed to a severe thermal load, the sagging or deflection measurement becomes an inevitable task from its safety/design analysis perspective. As an example, in a horizontal-type nuclear reactor safety study, it is required to measure the sagging of the channels during a postulated accidental scenario analysis. Unfortunately, measurement of the transient deflection/sagging of the channel under a harsh environment at extreme temperatures is a challenging task, and cannot be performed by the means of conventional intrusive approaches. This study proposes a non-contact digital imaging method with a laser generator and bandwidth filter, which is tested to measure the continuous channel sagging in a uniquely designed test rig. A scaled-down channel setup simulating the horizontal type nuclear reactor is used during the implementation of the present approach for sagging analysis at elevated temperatures. A digital edge detection tool with the Canny method is used to extract digital edges from recorded grayscale images, wherein successive images are used to measure transient sagging. The results are compared with post-test channel deflection measurements, and the difference in measurement is found to be within ±10 percent of post-test deflection.