Anu Pramila

Multiple Domain Watermarking for Print-Scan and JPEG Resilient Data Hiding

In this paper, we propose a print-scan resilient watermarking method which takes advantage of multiple watermarking. The method presented here consists of three separate watermarks out of which two are used for inverting the geometrical transformations and the third is the multibit message watermark. A circular template watermark is embedded in magnitudes of the Fourier transform to invert rotation and scale after print-scan process and another template watermark is embedded in spatial domain to invert translations. The message watermark is embedded in wavelet domain and watermark robustness in both approximation coefficient and detail coefficients is tested. Blind, cross-correlation based methods are utilized to extract the watermarks. The obtained success ratios were at least 91% with JPEG and JPEG200 quality factors of 80-100 and scanner resolution of 300dpi. The BER obtained with the previous settings was less than 1.5%.

Toward an interactive poster using digital watermarking and a mobile phone camera

A method for embedding a watermark in print media, posters or other paper printouts and reading the watermark information blindly with a camera phone is proposed. A subtractive-additive embedding method is applied in which the message is coded with a directed periodic pattern. The message is detected and read by searching regularities in the autocorrelation function of a periodic signal. The robustness to disturbance occurring during printing process due to air interface and camera phone properties is ensured using noise reduction, modified JND model, enhanced peak detection with filtering and shaping and two-level coding of the message. The validity of the approach is proven with tests, and an application example of an interactive poster is examined.

Image watermarking with feature point based synchronization robust to print-scan attack

In this paper we propose a content based multibit watermarking method robust to print-scan attack. A method to extract feature points, robust in terms of watermarking, is proposed. The location of the watermark is tied to a coordinate system defined by robust feature points. A message sequence is mapped to a directional angle of periodic patterns, which are scattered and embedded into triangles in permuted locations. In watermark extraction, an interplay between feature extraction and watermarking ensures reliability and a multibit message can be decoded blindly from the locations pointed by the key. By detecting the alignment of the autocorrelations peaks and using a coding table, a multibit message can be extracted. Experiments show that the method provides robust and blind extraction of watermark information after a print-scan attack and a set of compound attacks.

Reading Watermarks from Printed Binary Images with a Camera Phone

In this paper, we propose a method for reading a watermark from a printed binary image with a camera phone. The watermark is a small binary image which is protected with (15, 11) Hamming error coding and embedded in the binary image by utilizing flippability scores of the pixels and block based relationships. The binary image is divided into blocks and fixed number of bits is embedded in each block. A frame is added around the image in order to overcome 3D distortions and lens distortions are corrected by calibrating the camera. The results obtained are encouraging and when the images were captured freehandedly by rotating the camera approximately -2 - 2 degrees, the amount of fully recovered watermarks was 96.3%.

Image watermarking with a directed periodic pattern to embed multibit messages resilient to print-scan and compound attacks

In this paper, we propose a blind method to embed multibit watermarks in images, robust to various attacks on geometry and print-scan process. For carrying the multibit information, a method using directed watermark patterns is proposed. A message sequence is mapped to a directional angle of a periodic pattern, which is then embedded into image blocks. In the detection, using autocorrelation function, filtering, masking, and adaptive line search with Hough transform, the alignment of the autocorrelations peaks are detected from image blocks, and interpreted as a message. The method provides a robust and blind extraction of information after a print-scan attack. Additionally, the experiments with two laser printer and two printout material show that the method is robust to compound attacks, such as Stirmark random bending, shearing, aspect ratio change, cropping, translation, or JPEG combined with print-scan.

Watermark recovery from a dual layer hologram with a digital camera

In this paper we present a method for reading a watermark from a dual layer hologram image with a digital camera. Here the base of the hologram out of which the hologram was designed is a binary image. The hologram obtained is placed on a planar surface and an image is captured from the hologram by setting up a light source and a digital camera on appropriate distances and angles relative to the hologram. The captured image is corrected from affine distortions and a saliency detector based segmentation is performed for the image. The watermark is read from the resulting reconstructed binary image. The obtained results show that the watermark can be recovered perfectly from a dual layer hologram with a proper setting of the camera and light sources.

Wavelet domain print-scan and JPEG resilient data hiding method

In this paper we present a print-scan resilient method to embed multibit messages into images. Multilevel watermarking principles are applied in order to embed a reference watermark and the message bits. Methods to embed a robust spatial domain reference watermark, utilizing HVS are proposed and methods to improve the estimation of affine transformation parameters from a periodic reference watermark are considered. The multibit message is embedded on the approximation coefficients of the wavelet transform, utilizing JND profile estimation and additive spread spectrum techniques. A blind correlation based detection method is made use of to recover the message. In the experiments the imperceptuality issues related to multilevel watermarking are considered with different parameter settings and the robustness against print-scan attack and JPEG compression is measured and the results are shown.

Extracting watermarks from printouts captured with wide angles using computational photography

Thus far the research of print-cam robust watermarking methods has focused on finding new methods for embedding and extracting the watermark. However, the capturing process itself, has been neglected in scientific research. In this paper, we propose a solution for the situation when the watermarked image has been captured in a wide angle and the depth of focus of the camera is not deep enough to capture the whole scene in-focus resulting in unfocused areas. The solution proposed here relies on a subfield of computational photography, namely all-in-focus imaging. All-in-focus images are generated by fusing multiple images from the same scene with different focus distances together, so that the object being photographed is fully in focus. Traditionally, the images to be fused are selected by hand from the focal stack or the whole stack is used for building the all-in-focus image. In mobile phone applications, computational resources are limited and using the full focal stack would result in long processing times and the manual selection of images would not be practical. In addition, we propose a method for optimizing the size of the focal stack and automatically selecting appropriate images for fusion. It is shown here that a watermark can still be recovered from the reconstructed all-in-focus image accurately.

Increasing the capturing angle in print-cam robust watermarking

Abstract It is nowadays more probable that a print media is captured and shared with a mobile phone than with a scanner. The reasons for photographing the print range from intention of copying the image to simply sharing an interesting add with friends. Watermarking offers a solution for carrying side information in the images, and if the watermarking method being used is robust to the print-cam process, the information can be read with a mobile phone camera. In this paper, we present a print-cam robust watermarking method that is also implemented on a mobile phone and evaluated with user tests. Especially, the lens focusing problem when the picture is captured in a wide angle with respect to the printout is addressed. The results show that the method is highly robust to capturing the watermark without errors in angles up to 60° with processing times that are acceptable for real-life applications.

Improving Robustness of Biometric Identity Determination with Digital Watermarking

The determination of an identity from noisy biometric measurements is a continuing challenge. In many applications, such as identity-based encryption, the identity needs to be known with virtually 100% certainty. The determination of identities with such precision from face images taken under a wide range of natural situations is still an unsolved problem. We propose a digital watermarking based method to aid face recognizers to tackle this problem in applications. In particular, we suggest embedding multiple face dependent watermarks into an image to serve as expert knowledge on the corresponding identities to identity-based schemes. This knowledge could originate, for example, from the tagging of those people on a social network. In our proposal, a single payload consists of a correction vector that can be added to the extracted biometric template to compile a nearly noiseless identity. It also supports the removal of a person from the image. If a particular face is censored, the corresponding identity is also removed. Based on our experiments, our method is robust against JPEG compression, image filtering, and occlusion and enables a reliable determination of an identity without side information.