5. The method of claim 1 , wherein, determining whether there is a visual word in the visual dictionary matching the specific object comprises: comparing extracted local features of the specific object with local features of a visual word in the visual dictionary to obtain a local feature pair which comprises two identical or similar local features respectively extracted from the specific object and obtained from the visual word; calculating geometric distributions of the local features corresponding to the local feature pair, respectively in the specific object and in the visual word; determining whether the geometric distributions of the local features corresponding to the local feature pair, respectively in the specific object and the visual word, are consistent; considering the visual word as matching the specific object if the two geometric distributions are consistent.
5. The method of claim 1 , wherein, determining whether there is a visual word in the visual dictionary matching the specific object comprises: comparing extracted local features of the specific object with local features of a visual word in the visual dictionary to obtain a local feature pair which comprises two identical or similar local features respectively extracted from the specific object and obtained from the visual word; calculating geometric distributions of the local features corresponding to the local feature pair, respectively in the specific object and in the visual word; determining whether the geometric distributions of the local features corresponding to the local feature pair, respectively in the specific object and the visual word, are consistent; considering the visual word as matching the specific object if the two geometric distributions are consistent. 6. The method of claim 5 , wherein, before comparing extracted local features of the specific object with local features of a visual word in a visual dictionary, the method further comprises: combining the local features of each specific object to obtain a global feature; searching the visual dictionary for a candidate visual word with the most similar global feature with that of the specific object.