Kids will always tell you the truth. I have four daughters and I can't get a thing past them, especially all the stuff I seem to get past myself! I put up a heaviest-weight photo on my fridge too. I found an old thinn-er photo too that lives next to the fatty one. So that way I can see both of me and decide everytime I go the fridge which one I want to live with. No challenge there.
I can see it. What you should do is wear the same clothing and have your hair the same way as the first photo, etc. I bet the difference would jump out at you. I took some pics and when I hit the 50 lbs lost point I will take new pics wearing the same clothes. No one is seeing those pics until I hit that first goal though!!