In this short paper, the method of analyzing microchannel flow boiling phenomena by the image processing tool was briefly introduced. The experiments of subcooled and saturated flow boiling on various micro-/nanostructured modified surfaces were carried out. The high-speed images obtained from the experiments were taken as examples. Nucleated bubbles, partial dryout patches, and liquid–vapor interfaces could be recognized and quantified by the image processing tool. The transient statistical parameters of the region of interest (ROI) could be further obtained, such as the sequential equivalent diameter of bubbles and sequential area size as well as its spreading rate of dryout patches. The image processing tool was a valuable option to investigate microchannel flow boiling phenomena.