For the ones I had problems with, I opened them up in Paint Shop Pro, created 2 layers, put them over each other and hid/unhid the top layer to see what changed. Worked great although I know for a fact that I clicked where it said the difference was :(

Some of the levels actually change what the 5 differences are. So the 5 someone references above may not be the actual 5 differences when you load the game in your browser.