Confidential information included in image and voice data is filtered in an apparatus that includes an extraction unit for extracting a character string from an image frame, and a conversion unit for converting audio data to a character string. The apparatus also includes a determination unit for determining, in response to contents of a database, whether at least one of the image frame and the audio data include confidential information. The apparatus also includes a masking unit for concealing contents of the image frame by masking the image frame in response to determining that the image frame includes confidential information, and for making the audio data inaudible by masking the audio data in response to determining that the audio data includes confidential information. The playback unit included in the apparatus is for playing back the image frame and the audio data.