The GIPSA lab of INPG Grenoble organizes BOSS (Break Our Stegano System) challenge. Attackers will have access to a database of 1,000 pictures. Half of them are steganoed using a system called HUGO. The payload will be the same for every steganoed picture. Attackers have the source code of HUGO. The objective is to discriminate through steganalysis the stega pictures from the cover pictures.
The challenge is interesting. Regularly, the newspapers disclose story of unlawful people using steganography to hide message on the web. In these stories, the attackers/governmental agencies have not the advantages of knowing the used algorithms.
BOSS should remind you BOWS2. The GIPSA lab organized the same type of challenge but for watermark.