Just a few days after I posted about not being able to "see" continued weight loss, something in my head clicked over and I could see changes in my lower body. It wasn't a specific change, and I hadn't even lost more weight, but suddenly I recognized an alteration in overall shape which was reminiscent of how I looked after my large weight loss in college about 25 years ago. Since I was never thin, I never experienced a flat stomach (and don't expect that I ever will), but there was a difference in how my belly looked in terms of overall shape which I suddenly started to see emerge.
Body image is a curious thing because it is almost as if your brain is stuck on a certain look and tunes out the changes that are occurring for a certain period of time. This seems to make some sense for people who look at themselves in the mirror everyday and the changes come along gradually. In such cases, changes would be understandably imperceptible.
However, even someone like me, who has no full-size mirrors and does not inspect her body closely or often, cannot see the changes even when the appraisal is spaced out over weeks or even months. You'd think I'd see the changes more clearly because bigger changes might occur if one waits longer to look. The truth is that I have never known my body very well because I avoided getting to know it.
I think for a lot of overweight people, and especially those who become very, very fat like me, we disconnect as much as possible from our physical forms. It is more often than not the case that we "imagine" what we look like more than we might be aware. When you're avoiding having your picture taken, don't walk in front of reflective surfaces and wear clothes that stretch so that size changes are harder to detect, you don't really know how "big" you are. This means that you can't easily see how much smaller you are except by numbers on the scale (which I don't measure very often) or by rather large changes in form which take months, possibly up to a year, to come along.
There are other reasons why someone who is very big may find that they cannot see the changes well which make logical sense, such as the fact that the impact of 10 lbs. lost on a nearly 400 lb. body is not going to be as noticeable as that same amount lost on a 150 lb. body. However, I think many of us find our bodies so loathsome that we simply don't really "see" who we are when we begin to lose weight. If you don't have a really good idea of where you've started from, you have difficulty knowing how far you've come.