Hidden pictures – What is it?

A power point with 20 slides each with a picture hidden behind a numbered grid. Click on one square at a time to reveal part of the picture -how quickly can students guess what the object is? From a parking meter to a jet plane, from a pound note to a space craft.
Pictures: Airplane (jet plane -Boeing 747), Audio tape (cassette), Bicycle (‘Penny Farthing’), Car (Model T Ford), Coin (2 shilling piece) ,Computer (Commodore 64), European Union (flag), Fighter plane (Hawker Hurricane), Integrated circuit, NATO (symbol), Parking meter, Pound note, Record (45rpm single), Space lander (Apollo 11), Stamp (Postage), Telephone, Train (Steam locomotive), Typewriter, Union Flag, Video tape (for VCR)