For detection of oral potential malignant disorder (OPMD), devices such as VELscope, are potentially used in the oral cavity examination. The device area usually appears in the acquired images. A preprocessing stage, which consists of removing the device area, is required before the analysis of the images. In this paper we propose a method based on the Circular Hough transform (CHT) to detect auto fluorescence device part in the oral cavity images. The results revealed that the device area is successfully recognized whenever it is present in the image. © 2015 IEEE.