Secrets concealed using steganography are hard to find. You don't discern it visually or by file size. It's not part of the content that's been added to. It is the content. And steganography is not hard to do.
Several programs are available for download on the Internet.
But its results are impressive, hiding volumes of text in photographs without a visible trace. As far as Joe Blow off the street coming in contact with steganography, it looks innocuous. The classes are limited to federal law enforcement, U.S. intelligence agencies and Fortune 1,000 companies that can show a demonstrated need for the information. Al-Qaida is charged with blowing up two U.S. embassies in East Africa in 1998.