1. A multimodality-based image tagging apparatus, comprising: a memory; and a processor coupled to the memory and configured to execute instructions to: generate, for an inquiry image, a group of first scores about all tags in a tagging dictionary by using one or more training image(s) and multiple modalities of an image, wherein a group of first scores is generated for each modality; directly concatenate all the modalities of the image into a combined modality; generate, for the inquiry image, a group of second scores about all the tags by using the training image(s) and the combined modality; fuse the obtained multiple groups of first scores and the second scores to obtain final scores about all the tags, wherein the multiple groups of the first scores are linearly combined, and the second scores generated by using the combined modality are taken as constraint terms to lead to the linear combination for the final score to update the tag score; and select one or more tag(s) as tag(s) of the inquiry image according to the final scores about all the tags, wherein final score(s) of the selected tag(s) is/are larger than final score(s) of unselected tag(s).