A tamper detection method to protect the integrity of indexed color images is presented. This method generates authentication codes of the indices based on the pseudorandom number generator. The length of authentication codes can be adaptively chosen according to the user’s requirement. The authentication codes are embedded into the index table of the indexed color image. In the tamper detection procedure, the embedded authentication codes are extracted. Besides, the pseudorandom number generator with the specific random seed is used to generate another set of authentication codes. By means of comparing the two sets of authentication codes, the tampered areas of the indexed color images can be found. Experimental results show that the proposed method efficiently detects the tampered areas while keeping good image qualities of embedded images.