1. A resolution adjusting method, applicable to an image capturing device, wherein the image capturing device comprises a camera module and a storage unit, the resolution adjusting method comprising: capturing an image with a first resolution by the camera module; analyzing an amount of objects in the image, comprising: performing a recognition procedure to recognize and calculate an amount of subjects in the image; and determining the amount of the objects according to the calculated amount of the subjects; comparing the amount of the objects with at least one threshold value; when the amount of the objects is smaller than at least one of the at least one threshold value, lowering the resolution of the image from the first resolution to a second resolution according to the at least one threshold value, and storing the image with the second resolution in the storage unit; and when the amount of the objects is greater than or equal to the threshold value, storing the image with the first resolution in the storage unit.