With steganography being all the rage these days why not up the ante and use video as a covert channel? (I haven't looked around for this but I bet someone else is already doing it.) With all the bandwidth, and the data already being put through some sort of transcoding, the opportunity to embed seems ripe. I'm not sure how this would work, but let's assume the process is: (a) hardware camera, (b) software transcoding and compression of signal, (c) network traversal, (d) software transcoding and decompression of data, (e) video display. We'll assume adding data before (b) and extracting data after (d) will not work due to loss from the transcoding. To do live video stego insert a step between (b) and (c) to add data and between (c) and (d) to extract data. The method would be rather detectable. A better solution may be to drown yourself in transcoding and (de)compression code for a while and develop a stego (or stego capable) codec or a stego module for either a specific existing codec or any codec satisfying certain requirements. (Do these exist already?)
Embedding of small amounts of data should be difficult to detect. A simple (well, maybe) exercise would be to embed a chat in a video conference. Binary files, VoIP, other video conferences, multimedia files, or any sort of network traffic are all nice things to be able to embed.
The hardest needle to find is the needle you're not looking for.
(Relatedly, it would be desirable to be able to determine if someone has found your covert channel. How or if this could be done using lacking some sort of quantum crypto I'm not sure. Use of an additional channel to influence the convert channel in ways known by the covert parties might work but not be provably correct. The idea would be that when an ease dropper is present their would be some impediment to making the expected change in the channel, similar to quantum crypto. Although, "some impediment" is pointlessly vague.)