23. The apparatus of claim 14 , wherein the processor detects or allows another device to detect one or more text candidates while changing intensity levels of the pixels of a specific region in the specific image, and builds or allows another device to build a tree by allocating (i) a low-level text candidate whose intensity level in the specific region is relatively high and (ii) a text candidate whose intensity level is the highest among high-level text candidates whose intensity level in the specific region is relatively low, to a child node and a parent node, respectively, and wherein respective regions of the high-level text candidates include a region of the low-level text candidate.
24. The apparatus of claim 23 , wherein, if there occurs no less than a specific percentage of an overlap between at least one first region where at least one text candidate corresponding to at least one child node in the tree is included and at least one second region where at least one text candidate, with a relatively low intensity level of the pixel, corresponding to at least one parent node of the child node is included for no less than a specified number of times, provided that the second region is larger than the first region and includes the first region, the processor selects or allows another device to select at least one text candidate corresponding to the child node if difference between an area of a region of the text candidate of the child node and that of its parent node are relatively small; and wherein the processor classifies or allows another device to classify the weak text of the specific image as the strong text by referring to the information on the text classified as the strong text in the another image related to the specific image if more than the certain percentage of the detected text candidates are classified as the weak texts.