Difference circles distracting
SUGGESTIONS
The one solid change I would suggest, is to change the 'found difference' to being the same, instead of circling it. By circling, it distracts heavily from being able to notice differences, as well as excluding a region of the picture from any further differences, making it overall simple to find the remaining ones.
Adding some interesting audio would further assist enjoyability if chosen correctly.
Progressive differences - ie one that'll only appear after you've selected a couple already - will add to the challenge, and allow for getting more out of each slide.
The best I've seen in this genre included animation. It definitely added a depth of quality and a fresh approach by not simply displaying 2 static images.
REVIEW OF THE WORK ITSELF
The graphical alterations you've done in this production were good. There wasn't the obvious distortions from poor Photoshoping.
The buttons work as they should, though I'd suggest not using the gradient background of contrasting font colours, as it shows up like Comic Sans/Impact font or Lens Flare in Photoshoped images for someone new and inexperienced. Flash has some phenomenal tutorials on how to make your own buttons. You'll find it quick and easy to generate a Flash App that has your own unique look and feel, and a depth of quality that'll progress as you become more experienced. Also have a look at the plethora of sites with colour wheels displaying complementary colour schemes. Aesthetics is the key.
Good luck, and keep up with the designs!