I dont think people will be going around photographing everyone all the time in public places...I am just thinking that taking photos of buildings, streets, cars, etc. in everyday public places increases the odds that perhaps you will catch a suspecious character lurking about, or even in the act of a crime. The photo can then be used to identify, catch, or prevent a terrorist act. Like the article said, often times police ask the public to provide any information about a suspect, including any photos taken that might be valuable in finding the suspect or placing him at the scene of a crime.