1. A method for detecting a flame, comprising steps of: (a) capturing a plurality of images; (b) determining whether a bright object exists in the plurality of images, wherein the step (b) comprises sub-steps of classifying at least a specific pixel having components of Y, U and V as a bright pixel if the components of Y, U and V respectively meet predefined intervals; and grouping and labeling the bright pixel(s) to form a bright object; (c) analyzing whether the bright object is in a spatially flickering state, wherein the spatially flickering state comprises a state being one selected from a group consisting of: the bright object having an upper edge in a flickering state; the bright object simultaneously having an upper edge in the flickering state and a lower edge in a non-flickering state; and the bright object having an upper edge and a lower edge both in a flickering state, and the upper edge having a moving direction different from that of the lower edge; and (d) determining the bright object as the flame if the bright object is in the spatially flickering state.