Hi Luis,
it is difficult to work out what has gone wrong with so little information. Is your Moodle behind a firewall or a proxy? Is there some form of keyword filtering in place at your school? Did you upload the pictures from within the same network as you are looking at your pages now? For example, at my school the URL to get to Moodle from within the school is different to the one from outside of school - causing the pictures to be viewable only from the same 'place' as they were uploaded from. Could you please provide us with a screenshot of your issue?
Cheers,
Fred