Is it legal to photograph or video a TSA checkpoint at the airport?

Yes, mostly, it is legal as long as you don't interfere with operations or photograph the monitors.  According to the TSA's blog:

We don’t prohibit public, passengers or press from photographing, videotaping, or filming at screening locations. You can take pictures at our checkpoints as long as you’re not interfering with the screening process or slowing things down. We also ask that you do not film or take pictures of our monitors.

The TSA claims that, however, that there might be some unspecified local laws that may prohibit photography:

However… while the TSA does not prohibit photographs at screening locations, local laws, state statutes, or local ordinances might. Your best bet is to call ahead and see what that specific airport’s policy is.

Even if what you are doing is legal, the TSA still reserves the right to hassle you about it:

It’s important to note that we know there’s a difference between someone taking a casual photo and someone doing surveillance, but if you are taking pictures at or near the checkpoint, don’t be surprised if someone (TSA, airport police, or a curious passenger) asks you what you’re up to.

For supporting information on the general issue of the legality of photography,  U. Tenn. Law Prof. Glenn Reynolds recommends Morgan Manning’s excellent piece on photographers’ rights, as well as an article that he wrote with John Steakley: a due-process right to record the police.

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