Abstract
This article presents a semi-fragile image tampering detection method for multi-band images. In the proposed scheme, a mark is embedded into remote sensing images, which have multiple frequential values for each pixel, applying tree-structured vector quantization. The mark is not embedded into each frequency band separately, but all the spectral values (known as signature) are used. The mark is embedded in the signature as a means to detect if the original image has been forged. The image is partitioned into three-dimensional blocks with varying sizes. The size of these blocks and the embedded mark is determined by the entropy of each region. The image blocks contain areas that have similar pixel values and represent smooth regions in multispectral or hyperspectral images. Each block is first transformed using the discrete wavelet transform. Then, a tree-structured vector quantizer (TSVQ) is constructed from the low-frequency region of each block. An iterative algorithm is applied to the generated trees until the resulting tree fulfils a requisite criterion. More precisely, the TSVQ tree that matches a particular value of entropy and provides a near-optimal value according to Shannon’s rate-distortion function is selected. The proposed method is shown to be able to preserve the embedded mark under lossy compression (above a given threshold) but, at the same time, it detects possibly forged blocks and their positions in the whole image. Experimental results show how the scheme can be applied to detect forgery attacks, and JPEG2000 compression of the images can be applied without removing the authentication mark. The scheme is also compared to other works in the literature.
Highlights
The interest in remote sensing images has increased in the last few years
The Discrete Wavelet Transform (DWT) is a mathematical operation that converts an image into four sub-bands of information—HH, HL, LH and LL—that contain approximation coefficients (LL), detail middle-frequency coefficients (HL and LH), and detail high-frequency coefficients (HH)
By applying this first step of the scheme, blocks of 64×64 pixels of the hyperspectral image with similar entropy are combined in one large block
Summary
The interest in remote sensing images has increased in the last few years. New applications of this type of images are continuously being reported. Most of the existing semi-fragile watermarking schemes are designed for grayscale or RGB images, and these can be applied to each separate spectral band of remote sensing (hyperspectral or multispectral) images. If tampering localization is required, a hashing algorithm can be applied blockwise, but the amount of side information will significantly increase, since a different hash value would be required for each block This side information needs to be protected, e.g., by using digital signatures, to prevent malicious attacks. A semi-fragile watermarking scheme is proposed in [10] in which a hyperspectral image is used for embedding the watermark to provide tamper detection by using vector quantization approach. A tree of endmembers (the values obtained by the remote sensor for each pixel) is constructed These endmembers are transformed using the DWT to provide robustness against near-lossless compression.
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