We present an automatic method for measuring the tone response curve of display devices based on visual methods, where the eye is replaced by an end-user, uncalibrated camera, such as a webcam. Our approach compares a series of halftoned patches of known covering ratio with a continuous series of tone patches for each ratio. Both patches are shot by a camera that is used as a virtual eye to evaluate the luminance difference. By an iterative process, the continuous tone value is adjusted while compared with the perceived level of the halftoned patch. When the camera does not see any difference between the patches or a minimal difference, the luminance level of the continuous patch corresponds to the relative luminance of the halftoned patch covering ratio. We demonstrate that the method is as accurate as an equivalent visual method. The advantage of using a camera over the human eye is due to the limitation of observer variability while performing visual tasks.