Whitepaper that goes into detail on the steps necessary to hide and extract uuencoded files leveraging EXIF comments and third party sites like Facebook that fail to strip the data.
You can download it from the following link: https://packetstormsecurity.com/files/download/98514/Embedding_hidden_files_in_jpeg_and_abuses.pdf
Source: https://packetstormsecurity.com/files/98514/Embedding-Hidden-Files-In-Jpeg-Images.html