1. A hand-positioning method used in a human-computer interaction system comprises: continuously capturing a current image of a monitored display area so as to obtain a sequence of video images including a foreground object; extracting a foreground image from each of the obtained video images, and then carrying out binary processing with regard to the extracted foreground image so as to obtain a binary foreground image; obtaining a set of vertexes of a minimum convex hull of the binary foreground image, and then creating areas of concern serving as candidate hand areas by letting the respective vertexes of the minimum convex hull of the binary foreground image be central points of the areas of concern; and extracting hand imaging features from the respective created areas of concern, and then determining a hand area from the candidate hand areas by carrying out pattern recognition based on the extracted hand imaging features, wherein the binary processing carried out with regard to the extracted foreground image includes: calculating an edge image of the extracted foreground image; calculating a gradient image of the extracted foreground image, and then carrying out binary processing with regard to the gradient image so as to obtain a first binary result; carrying out binary processing with regard to the extracted foreground image by using a predetermined threshold value so as to obtain a second binary result; combining the edge image, the first binary result, and the second binary result by using an OR logical operation so as to obtain a new binary image; and filling a closed area in the obtained new binary image.