Taking Pictures at TSA Checkpoints is LEGAL

"TSA does not prohibit the public, passengers or press from photographing, videotaping or filming at security checkpoints, as long as the screening process is not interfered with or slowed down. We do ask you to not film or take pictures of the monitors. While the TSA does not prohibit photographs at screening locations, local laws, state statutes, or local ordinances might.

Taking photographs may also prompt airport police or a TSA official to ask what your purpose is. It is recommended that you use the Talk To TSA program on tsa.gov to contact the Customer Support Manager at the airport to determine its specific policy. Or, if you are a member of the press, you should contact the TSA Office of Public Affairs."

http://www.tsa.gov/traveler-information/taking-pictures-checkpoint