In this paper we describe a new system for storing annotated images in a large database and querying by means of a dynamical retrieval of images through use of metadata. It is based on a three-tier architecture suitable for building a common gateway for accessing heterogeneous data. Based on XML schema of documents, the extraction of metadata is used for successive querying. We give an example on a database of astronomical and geographical images, but the method is quite general and can be applied to more general case of large heterogeneous databases.
In this paper we present a novel digital watermarking technique for still image authentication. A model of the Human Visual System is exploited not only to enhance the visual quality of the watermarked images, but also to enhance the receiver’s probability of extracting the watermark correctly. Our goal is to jointly optimize rate, robustness and visibility, so that detailed features can be embedded, content-preserving manipulations are tolerated and the authenticated image is not distorted too severely by the embedding process. The algorithm performance has been assessed through numerical simulations and comparisons with the current state of the art. Results prove significant improvements in robustness against perceptually lossless modifications (such as mild JPEG and JPEG2000 compression).