1. An information processor which detects factors, in a video, influencing health, comprising: an image input unit which receives a series of image data to process a plurality of consecutive still images constituting the video; a feature-quantity calculation unit which calculates a feature quantity of each of the still images on the basis of the image data; a conditional-expression storing unit which stores a conditional expression, for each factor, to determine whether each of the still images produces the factor on the basis of the corresponding feature quantity; a factor determination unit which determines, for each factor, whether each of the still images produces the factor on the basis of the corresponding feature quantity and the corresponding conditional expression; an image-list display unit which displays, for each factor, a list of information indicating the still images determined to produce the factor; an image-storing unit which stores the series of image data received by the image input unit, wherein the feature quantity is divided feature information obtained by using feature quantities of divided images, the divided images obtained by dividing each of the still images in a grid-form, and the conditional expression is to determine whether the number of particular divided images among the divided images exceeds a predetermined threshold, the particular divided images each having the divided feature information that has a difference from that of the corresponding divided image of each of the consecutive still images, the difference exceeding a predetermined threshold.