I understand even if a person is cautious, there are ways that others can out his/her secrets. In many cases, reporters will catch public figures in compromising situations. This guy volunteered his picture, with metadata on it, to a complete stranger. That is the reason for the question on the title of the thread.
The article at the gossip site, Gawker.com contains the details to the story;
http://gawker.com/#!5755071/married-gop-congressman-sent-sexy-pictures-to-craigslist-babe
The resignation story on Fox News.
http://www.foxnews.com/politics/2011...to-craigslist/
His website and statement:
http://chrislee.house.gov/index.cfm?...76&itemid=1392
My only observation, he forgot to show a "duck face" when taking that picture