some images won't display in hotmail


New Email
A few weeks ago for no (apparent) reason, my sister's hotmail acct. started showing the little gray box with the x in it instead of displaying some images.
What caused this and more importantly, how do you change it back. I'll need to pass the answer on to her so it's GOT to be in simple terms as she is NOT adept at this type of thing. I use Outlook Express so I'm not familiar with hotmail at all. TIA