|Let me try using my psychic abilities here...|
You are in a classroom setting and you have all downloaded this jpeg file from a server. On two machines, the file won't open with the default viewer, while other machines open the file without problems.
If the above is basically the situation, the file may have become corrupted while being downloaded onto the two problem machines. Try downloading the file again.
Please let us know if you found someone's advice to be helpful.