Until now, an image imaged by a DSC (digital still camera) or a digital video camera was simply used to be viewed personally.  Recently, such an image is also used to be browsed by random people through a web site or a blog.  However, an image imaged by an individual includes information capable of specifying the individual or an area, such as a person, a vehicle, an indicator indicating a imaged area, or the like.  Accordingly, it is difficult to protect privacy of the individual if the image is open to the public as it is. 
In order to protect the privacy of the individual, a mask process (a mosaic process, a fog process, a coloring process, or the like) may be performed on the person, the vehicle, the indicator, or the like that specifies the individual or the area, from the obtained image.  For example, the person may not be specified by performing face detection and performing the mask process on an image of a face part, or the vehicle may not be specified by performing the mask process on a character information part of a number plate, or the area may not be specified by performing the mask process on an indicator part, such as an address, a school name, a station, a store, or the like.  A technology of performing a mosaic process on such a face part image which is part of the image, is known (for example, Patent Document 1).  However, since the face part is detected based on a skin color part in the image in such a technology, the mosaic process is performed with respect to all imaged face images.  Accordingly, individual setup of privacy protection, such as performing the mosaic process only on a certain person or performing the mosaic process on everybody except for a certain person, could not be made by using such a technology. 
Accordingly, a technology of performing a mosaic process only when a detected face image and a pre-recorded face image of a certain person are identical is disclosed (for example, Patent Document 2).  In such a technology, not only face color detection, but also methods called extraction of difference with a background image, pattern matching, and extraction of face-likeness are used for face detection.  Also, the precision for specifying a face is increasing since feature points such as an eye, a nose, a mouth, an ear, etc.  are used as features for specifying a face after detecting the face, and resolution of a video signal (image signal) is improved.  Recently, the protection of privacy of the individual is more precisely promoted as it became possible to perform the mosaic process not only on the face part, but also on character information of the number plate or character information specifying the area by comparing the character information through an OCR technology or pattern matching. 
(Patent Document 1) Japanese Laid-Open Patent Publication No.  2001-086407
(Patent Document 2) Japanese Laid-Open Patent Publication No.  2004-062560