1. An image analysis apparatus for detecting a periodic signal corresponding to an arrangement of a grid, which is required to reduce scattered radiation components from an object, from an image obtained by radiation imaging using the grid, said apparatus comprising: a setting unit configured to set a plurality of regions on the image; an obtaining unit configured to obtain statistic information of pixel values corresponding to each of the plurality of regions of the image based on the image; a selection unit configured to select at least one measurement region from the plurality of regions based on the statistic information; and a detection unit configured to detect the periodic signal using image data of the selected measurement region.