Philips impossible object ads

These impossible objects were popular a couple of decades ago though the ideas had been around for years through the graphic art of Dutch artist MC Escher and Swedish Oscar Reutersvard who designed these ads for Philips.  I found the five in The Economist magazine during 1986, each was part of a spread with the right-hand page singing the praises of the companies problem solving capability.  
     The clever little Lego piece was probably Photoshopped.  Google impossible objects to see plenty more.