Photo's on Websites with ? marks

New to these forums as well as new with a Mac. On a few websites when I look at pictures that were added especially in forums some pictures don't open and they are just a question mark in a little blue box. If anyone has any tips or help i'd greatly appreciate it. Sorry to start a whole thread for this.. Was not sure where to find this questions..

thanks

Can you give us a few URL's so we can test them and see what is up?

Sounds like a firewall issue, some images are blocked and you get the red box with an X through it or the ?.