> It looks I am unable to use HTtrack correctly
> because I,just want to grabber all the hidden
> pictures from
> <http://static.nfl.com/static/content/public/pg-photo>

Since your browser can't read that directory, neither can HTTrack. There is no
magic here.

If you don't have the URLs then you can only spider the site to get what is
published. Hidden pictures = unpublished = UNKNOWN.