1. A method for providing thumbnail image data on a mobile terminal, comprising: determining whether an image management mode is selected when the mobile terminal is in a standby mode; analyzing bit streams of a plurality of stored actual images to obtain picture sizes and compression ratios of the actual images upon selection of the image management mode; extracting Discrete Cosine Transform (DCT) coefficients at certain blocks of the bit streams of the actual images based on the obtained picture sizes and compression ratios; and partially decoding the extracted DCT coefficients, reducing the partially decoded DCT coefficients at a predetermined rate for generating thumbnail images of the plurality of actual images and displaying the generated thumbnail images.