Schneier on Security:

Since 9/11, there has been an increasing war on photography. Photographers have been harrassed, questioned, detained, arrested or worse, and declared to be unwelcome. We’ve been repeatedly told to watch out for photographers, especially suspicious ones. Clearly any terrorist is going to first photograph his target, so vigilance is required.

Except that it’s nonsense.
The 9/11 terrorists didn’t photograph anything. Nor did the London
transport bombers, the Madrid subway bombers, or the liquid bombers
arrested in 2006. Timothy McVeigh didn’t photograph the Oklahoma City
Federal Building. The Unabomber didn’t photograph anything; neither did
shoe-bomber Richard Reid. Photographs aren’t being found amongst the
papers of Palestinian suicide bombers. The IRA wasn’t known for its
photography. Even those manufactured terrorist plots
that the US government likes to talk about — the Ft. Dix terrorists,
the JFK airport bombers, the Miami 7, the Lackawanna 6 — no
photography.