Illustration Watermarks for Vector Graphics
PG '03 Proceedings of the 11th Pacific Conference on Computer Graphics and Applications
Nested object watermarking: from the rectangular con-straint to polygonal and private annotations
Proceedings of the 9th workshop on Multimedia & security
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In this paper, we introduce to the special domain of image annotation watermarking, based on embedding of hierarchical data related to objects into user-selected areas on an image. In comparison to earlier methods, the main goal of the work presented here is to provide a specific robustness, specifically against cropping, in a way that preserves hierarchical object relations even after retrieval from a partial image, which has been cut from the original (pure security aspects are of limited relevance for our application). We identify two initial categories for such relations, visual-functional and visual-spatial and suggest a novel coding scheme for the first of these. Our prototypical system consists of a new ontology-based interactive editor and a watermarking scheme, which is an extension of previously suggested block-based image watermarking towards the specific requirements for annotation watermarking. Our initial experiments of the new approach include evaluation of appropriate synchronization patterns and issues of their threshold-based exhaustive search. Further, we present results from robustness tests, which are based on cropping and lossy JPEG compression. Our findings show that the suggested method is capable to restore payload in a hierarchy-preserving way after up to 50% JPEG compression, with a low to medium loss of transparency, which has been evaluated subjectively. Further, we observe that even when limiting exhaustive search to those watermark candidates showing the highest embedding energy, we are able to correctly detect between 55% and 100% of cropped objects.