1. A computer-implemented method for diet management, adapted to a diet management system comprising a computer and a memory device used as a database, the computer comprises a processor and a plurality of program instructions, wherein the plurality of program instructions are loaded into the processor to perform the computer-implemented method, and the computer-implemented method comprising: capturing at least one diet image via an image capture device; pre-processing the at least one diet image so as to obtain at least one diet region from the at least one diet image and obtain at least one detailed food segment from the diet region; extracting at least one diet image feature from the at least one detailed food segment; generating a supervector based on the at least one diet image feature; performing similarity comparison between the supervector and at least one feature vectors in the database to determine a diet type of the at least one detailed food segment and to determine at least one similar population; providing information related to the similar population; and providing a personal diet characteristic analysis based on the diet type and an area of the at least one detailed food segment, wherein the providing the information related to the similar population comprises: calculating at least one statistic of the similar population by using at least one multidimensional data of the similar population; and providing the information related to the similar population based on the statistic of the similar population.