Image synthesis device and image synthesis method

An image synthesis device comprising:

• a first illumination light source configured to illuminate an object to be detected;
• a second illumination light source disposed at a different position from the first illumination light source and configured to illuminate the object to be detected;
• a light source controller configured to alternately turn on the first and second illumination light sources;
• a photographing section configured to photograph the object to be detected while the first illumination light source is turned on to generate a first image in which the object to be detected is present and configured to photograph the object to be detected while the second illumination light source is turned on to generate a second image in which the object to be detected is present;
• a storage section configured to store therein a first reference image generated by photographing a photographing range of the photographing section under conditions where the first illumination light source is turned on and where the object to be detected does not exist in the photographing range and a second reference image generated by photographing the photographing range under conditions where the second illumination light source is turned on and where the object to be detected does not exist in the photographing range;
• a difference image generation section configured to generate a first difference image based on a difference between the first image and first reference image and a second difference image based on a difference between the second image and second reference image;
• and
• a synthesis section configured to synthesize the first and second difference images to generate a synthetic image.