I had a little start-up idea a while ago .. albeit only tangentially related to this one.<p>Make a deal with JC Decaux, or some similar out-of-home advertising company to place cameras (strategically) around the City of London.<p>Nominally to provide personally tailored advertising, the significant secondary purpose is to use face recognition to identify individuals-of-interest: specific traders, fund managers and so on.<p>This enables us to analyse facial expression, gait, maybe body temperature to determine mood, then look for correlations in the stocks and markets that these individuals trade.<p>I think that this will be legal, since all the information that you are using is (nominally, at least) legal, and gained in a public place.<p>After all, if it is OK for the authorities to place the whole population under close surveillance, they cannot possibly object if we turn around and do the same thing to their paymasters, can they?