1. An image pickup apparatus comprising: an optical section configured to form an image of light beams from one person or plural objects; an image sensor configured to pick up the image formed including one or plural pictures of one or plural persons as the objects; a temporary recording memory; an operation section configured to set photographing operation modes including a best shot synthesis mode, and configured for operation input for photographing a still image by a user; a signal processor comprising: an acquisition section configured to sequentially acquire first images including the one or plural pictures of one person or plural persons, the one or plural pictures being outputted from the image sensor, wherein the temporary recording memory is configured to sequentially buffer the first images sequentially acquired by the acquisition section; a first image processor configured to sequentially perform, on the first images in the temporary record memory, an image processing that causes the first images to be adapted for sequential live view display or an image data recording format at the time of photographing, and generate a second image which is a photographed image; a feature determining section configured to determine, from the second image, presence or absence of the one or plural pictures of one or plural persons, and an aspect of the one or plural picture of the one or plural persons; a second image processor configured to perform, on the first images in the temporary record memory, a trimming processing that extracts a partial region of the one of plural pictures of one person or plural persons, when a result of determination by the feature determining section shows presence of the one or plural pictures of one or plural persons, and generate one or plural partial images; a best shot image detection section configured to select, from among the one of plural partial images, one or plural best shot images to be synthesized with the second image, on the basis of the number of detection of the one or plural pictures of one or plural persons and of an aspect of the one or plural pictures of one or plural persons determined by the feature determining section; an image synthesis section configured to perform, on the second image, synthesis processing of synthesizing an image serving as a synthesis frame and the one or plural best shot images selected by the best shot image detection section, and generate a third image as an image subjected to the synthesis processing; an image selection section configured to select one of the second and third images in accordance with a setting of the photographing operation mode through the operation section and a result of determination by the feature determining section, and output the selected image as a fourth image which is a recorded image, the image selection section selecting the third image and outputting the selected third image as fourth image when the photographing operation mode set through the operation section is the best shot synthesis mode, an operation input for photographing a still image has been made by the user, and the feature determining section has determined the one or plural pictures of one or plural persons from the second image, and otherwise selecting the second image and outputting the selected second image as the fourth image; and a display controller configured to transmit a display control signal based on the fourth image processed to be selected and outputted by the selection section; and a display configured to display and output a display image based on the control signal from the display controller, wherein the third image is an image in which the synthesis frame is synthesized in an upper region of the second image, and in which a synthesis processing has been performed for arranging the best shot image in a region corresponding to the synthesis frame.