Method for constructing a composite image incorporating a hidden authentication image

A non-transitory computer-readable medium having software code stored thereon, the software code being configured to cause a computer to execute a method for constructing a composite image having an authentication image formed therein, the authentication image being viewable by placing an object to which the composite image has been applied over a decoder lens having a plurality of lens elements defining one or more decoder lens frequencies, the method comprising:

• generating two gray-scale component images having tonal areas that are tonally balanced around at least one tonal value, at least one of the two gray-scale component images being configured to include a representation of the authentication image;
• determining a first pattern of the component image elements for the two gray-scale component images, the first pattern including a first element configuration and at least one element frequency that is equal to or a multiple of one of the decoder lens frequencies, the component image elements for a corresponding gray-scale component image collectively carrying content of the corresponding gray-scale component image;
• extracting at least a portion of the content from the component image elements of the two gray-scale component images;
• and
• constructing a composite image having a second pattern of composite image elements, the second pattern having a second element configuration that corresponds to the first element configuration, the second pattern having the at least one element frequency that is equal to or a multiple of one of the decoder lens frequencies, the composite image elements including the content extracted from the component image elements obtained from the two gray-scale component images.

An authenticatable object comprising:

• a surface configured for receiving a composite security image;
• and
• a composite security image applied to the surface, the composite security image comprising:
• a plurality of composite image elements comprising subelements defining content extracted from component image elements of two gray-scale component images, the two gray-scale component images having tonal areas that are tonally balanced around at least one tonal value, at least one of the two gray-scale component images being configured to include a representation of an authentication image;
• a first pattern of the component image elements for the two gray-scale component images, the first pattern including a first element configuration and at least one element frequency that is equal to or a multiple of one or more decoder lens frequencies, the component image elements for a corresponding gray-scale component image collectively carrying content of the corresponding gray-scale component image;
• and
• a composite image having a second pattern of the composite image elements, the second pattern having a second element configuration that corresponds to the first element configuration, the second pattern having the at least one element frequency that is equal to or a multiple of the one or more decoder lens frequencies, the composite image elements including content extracted from the component image elements obtained from the two gray-scale component images,
• the authentication image being viewable through a decoder lens placed over the composite security image.