Ravi Bhargav, Priyanka Singh
Unmanned aerial vehicle (UAV) images are widely used in surveillance, remote sensing, disaster monitoring, and infrastructure inspection. Motivated by the need for secure transmission of such aerial images, this paper proposes a block-wise image authentication method that can detect not only image modification, but also block swapping, relocation, and copying from another image. This is important because many existing methods mainly verify pixel values and may fail when a visually valid region is moved from its original position. The proposed method divides the image adaptively, so detailed regions are represented by smaller blocks and smooth regions by larger blocks. Similar neighbouring blocks are then grouped, and a structure-based reference is formed from both their visual properties and spatial arrangement. This reference is linked to the position of each block, so that moved or copied blocks fail verification before decryption. Experiments on 1000 grayscale and colour images with resolutions from 256 × 256 to 2048 × 2048 achieved an overall tamper-detection rate of 98.9%, localisation accuracy of 98.2%, and a false positive rate of 1.3%. The method also preserved high reconstruction quality, reaching up to 37.45 dB PSNR and 0.9993 SSIM, while the required authentication data remained nearly constant across image sizes. These results show that the proposed method provides reliable tamper localisation and secure verification for practical image transmission.