1. An imaging apparatus comprising: first imaging control means for performing periodic imaging; first detection means for detecting a predetermined photographic subject from image data imaged by the first imaging control means; instruction means for instructing imaging a still-image during the periodic imaging by the first imaging control means; second imaging control means for imaging a still-image when instructed by the instruction means; second detection means for detecting a predetermined photographic subject from still-image data imaged by the second imaging control means; comparison means for comparing a result of the photographic subject detection by the first detection means with a result of the photographic subject detection by the second detection means; and informing means for informing of a comparison result by the comparison means.