1. A method for recognizing plant diseases, comprising: providing a plant disease database, for storing at least one plant disease and at least one piece of disease characteristic image corresponding to each plant disease; obtaining a piece of plant image by an image capture device; analyzing the plant image to obtain a piece of segmented plant image by an image processing unit according to a first processing technique, and analyzing the segmented plant image information according to a second processing technique to obtain at least one suspected region image; calculating the area of each suspected region image, and when the area is greater than a preset threshold, taking the suspected region image as a piece of syndrome image; and comparing the syndrome image with at least one piece of disease characteristic image in the plant disease database, and when the syndrome image matches a piece of specific disease characteristic image in the at least one piece of disease characteristic images, reporting a specific plant disease corresponding to the specific disease characteristic image.