1. An information processing apparatus for assigning metadata to a target image content by using a processor, the information processing apparatus comprising: a storage unit configured to store a plurality of image contents with metadata assigned thereto; a first acquisition unit configured to acquire an image feature amount of the target image content; a similar image search unit configured to perform a similar image search by searching the plurality of image contents stored in the storage unit for image contents having a similar image feature amount to the image feature amount of the target image content; a second acquisition unit configured to acquire at least one metadata assigned to any of the image contents obtained as a search result of the similar image search; a selection unit configured to sequentially select one of the at least one metadata acquired by the second acquisition unit; a metadata search unit configured to perform a metadata search for the selected metadata by searching the plurality of image contents stored in the storage unit for image contents having the selected metadata; a calculation unit configured to calculate an overlap ratio of the image contents obtained as the search result of the similar image search and the image contents obtained as a search result of the metadata search for the selected metadata; and an assignment unit configured to assign the selected metadata to the target image content if the overlap ratio for the selected metadata exceeds a threshold.