1. A method for producing a stereo image of an object with using a multi-camera portable device having at least two image sensors, at least a first one of said image sensors being arranged on a first face of the portable device and a second one of said image sensors being arranged on a second face of the portable device opposite to the first face thereof, the method comprising the steps of: arranging the object in front of the first image sensor so that the object falls within the field of view of the first image sensor, arranging an external mirror in front of the second image sensor so that a mirrored view of the object and a mirrored view of the portable device fall within the field of view of the second image sensor, substantially simultaneously recording, by the first image sensor, a first initial image containing a picture of the object, and by the second image sensor, a second initial image containing (i) a picture of the mirrored view of the object appearing in the mirror and (ii) a picture of at least a portion of the mirrored view of the portable device appearing in the mirror, thereby producing an initial pair of images, finding the center of the picture of the mirrored view of the second image sensor within the second initial image, determining the distance ratio of a first distance between two points of the portable device in reality and a second distance of the respective points in the second initial image for obtaining the direction and the length of a mirroring vector, which points from the center of the second image sensor to the center of the virtual second image sensor, obtaining a capturing focal length of the second image sensor, and by using said mirroring vector and the capturing focal length of the second image sensor, transforming the coordinate system of the first image sensor into the coordinate system of the virtual second image sensor to generate a stereo image pair from the first initial image and the second initial image for the object.