基于块分类编码的电子发票图像自恢复水印算法

兼顾水印容量以及篡改图像的恢复效果，提出一种基于块分类编码的电子发票图像自恢复水印算法。根据电子发票的特性将图像块分为重要块、印章块、格式块和空白块4类。对图像块类型和非空白块二值化信息分别利用RS（1，3）和RS（2，3）进行编码生成恢复水印。根据恢复水印信息的大小，基于密钥将生成的恢复水印随机、依次嵌入印章块、格式块和空白块中。为尽可能降低水印容量，无需添加认证水印数据，利用类型码和非空白块恢复水印，同时完成对图像的篡改检测以及篡改恢复。与现有的用于自然图像的自恢复水印算法相比，在相同水印容量下能得到较好的恢复效果；对于同样的恢复效果，水印容量较小。在一般篡改和拼贴攻击下具有较好的认证和恢复能力。

Self-Recovery Watermarking for e-Invoice Image Based on Block Classification and RS Coding

Taking into account watermark size and quality of recovered image that was tampered, this work proposes a self-recovery watermarking algorithm for e-invoice images based on block classification coding. Image blocks in a test e-invoice image are classified into four types: blocks containing important contents, seal, and invoice format information, and blank ones. The block types and the binary information of all non-blank blocks are coded with RS(1,3) and RS(2,3) respectively to generate a recovery watermark. Based on a key, the recovery watermark is randomly embedded into the blocks in an order of seal, format, and blank until all watermark data are used up. To minimize the size of watermark, the recovery watermark based on the type code and binary information code is used for both authentication and image recovery without additional authentication information. Compared with the recent self-recovery approaches for natural images, the proposed method gives better recovery quality with the same watermark size, and produces a smaller watermark with the same recovery quality, and has better performance both in tamper detection and image recovery against general tampering as well as collage attacks.