Both good points [sepia imagery at beginning and then the reference to the song], here are some quick others:
- the characters are exceedingly imaginary...a talking scarecrow, lion and tinman, a wicked witch of the west, a good witch of the north, the violent talking trees who throw apples at people [lol] and those ugly little winged gremlins... nothing realistic about any of these characters _ do NOT mention the spastic dog Toto, there is nothing imaginative about him and i have heard a fair few people missed out on marks for naming him as one of the imaginary characters, because the markers think the person did not research the source correctly or thoroughly enough...stupid, i know!
- the obstacles and the ways that they are faced show a sign of imagination; for example: the wicked witch summons a paddock full of flowers with sleeping powder, the sudden appearances out of no-where by the witch, dorothy, the tinman, lion and scarecrows narrow escapes within the castle which is heavily guarded and then, of course, the "melting" of the witch due to the splash of water
- the composed sing-song characteristics that are evident every half-and-hour of so within the movie; the songs represent emotion, for example: "somewhere over the rainbow" represents hope and longing, "Off To See The Wizard" represents hope, happiness and excitement and "If I Were King Of The Jungle" represents excitement, optimism and courage/bravery.
- the fact that when dorothy wakes up, everything is back in the sepia colour [sepia, in case you're confused, is the brownish colouring of images instead of having it in black and white_less "old school" lol] showing her return from the dream/fantasy land back into reality
there are many more ideas which can be put into your final answer, a good website which has ALOT of information about "The Wizard Of Oz" is
http://www.geocities.com/Hollywood/hills/6396/ozfromaz.htm, check it out it's pretty detailed and analytical
Infinity111