Batch Steganography and Pooled Steganalysis

Conventional steganalysis aims to separate cover objects from stego objects, working on each object individually. In this paper we investigate some methods for pooling steganalysis evidence, so as to obtain more reliable detection of steganography in large sets of objects, and the dual problem of hiding information securely when spreading across a batch of covers. The results are rather surprising: in many situations, a steganographer should not spread the embedding across all covers, and the secure capacity increases only as the square root of the number of objects. We validate the theoretical results, which are rather general, by testing a particular type of image steganography. The experiments involve tens of millions of repeated steganalytic attacks and show that pooled steganalysis can give very reliable detection of even tiny proportionate payloads.