Remember the sixties when any robots that menaced you could be destroyed by feeding them a logical paradox? They would fizz and spark, then their voices would get slower and slooowwwweerrrr as though their internal phonographs had wound down. I'm pretty sure it happened on Star Trek at least once. That's what this Pop Art exhibition at the National Portrait Gallery reminds me of. Works of art which were made by tweaking and fiddling with other people's trademarks and copyright images - and you're not allowed to photograph them because that would infringe the tweaker's copyright. Read about it here. The more I think about intellectual property law and the way it gets applied, the more I get the urge to repeat, 'Danger! Danger! Will Robinson' over and over to myself.