The hints are right above you.
The Mickey's are all on the facebook pages. The contest gives you the list of each page to look at. Most of them are in the photo albums. Go the page, click photos, then click the links for albums. The albums that say "updated last thursday" have the images hidden.
You can also mouse over the picture rather than open them and the description will say "congratulations you have found a hidden Mickey". Open that picture then click on the link to claim the hidden Mickey.
Look in the shared memories photos as well.
One other hint- Star Tours is the only facebook page that has one for each contest. PP you are now registered for both the WDW and DL contests. They are separate.
I found all 20 in about 15 minutes with the above information.
good luck.