@rye it's not dumb.  "dumb" is if you don't ask the question ...

wikipedia's def isn't bad: "[..] OPSEC is the process of protecting individual pieces of data that could be grouped together to give the bigger picture (called aggregation). OPSEC is the protection of critical information deemed mission essential from military commanders, senior leaders, management or other decision-making bodies. The process results in the development of countermeasures, which include technical and non-technical measures such as the use of email encryption software, taking precautions against eavesdropping, paying close attention to a picture you have taken (such as items in the background), or not talking openly on social media sites about information on the unit, activity or organization's Critical Information List."

in a nutshell, though, most of us recommend not putting up pictures of yourself in your avi or tl for the public to see, or otherwise revealing information would make you personally identifiable for someone sufficiently motivated.