Image acquisition proceeds in three phases, namely optical coupling, image sensing, and signal conversion, resulting in the perspective image, sensed image, and acquired image, respectively. The asynchronous signal conversion between video camera and image grabber elicits the phase drift, a limiting factor of the image resolution. We pioneer in experimentally verifying the existence of random phase drift, contribute to estimating the phase-drift-induced mensuration uncertainties, and explore a low-cost detection method that identifies the phase drift at the subpixel level. Experimental results are reported. A frame-by-frame compensation method for the phase drift of each scan line, which employs the proposed detection method, is suggested.