A method of operating a workstation includes capturing multiple monitoring images each being captured with the imaging sensor while the illumination light source is energized during one of multiple short exposure-time-periods, and detecting a checkup-condition that includes analyzing the multiple monitoring images to determine the presence of any adverse feature on workstation's window. Each of the multiple short exposure-time-periods is shorter than four times of a threshold exposure-time-period but no shorter than 25% of the threshold exposure-time-period. The threshold exposure-time-period is a minimal exposure-time-period needed for the imaging sensor to capture recognizable patterns of a barcode that is in directing contacting with the window while the illumination light source is energized.