It depends upon your version of FP, and what the type of image is. If
they're JPG images, it could be that some of them are in a progressive JPG
format. Some versions of FP had difficulty displaying a progressive JPG in
the designer like what you are describing.
Hope this helps,
Mark Fitzpatrick
Microsoft MVP - FrontPage
I was able to get my page to work after I tripped over a refresh button. A
new browser opened and voila there it was. I did change to a smaller image
on another that was not showing and that seemed to do the trick with that
file as well.
I am using Frontpage 2003.