JOSE:
It probably worked for you yesterday because your browser probably had the imaged cached. The links do not work because of how your web site server works. The logic behind sites.uol.com.br is disallowing indirect access to content posted on your pages. Direct accesses are allowed and that is why pasting the links into the browser address box works.

Note I made a comment about where it may not be desirable to host images last week in this post ->
http://www.8052.com/forum/read.phtml?id=59651 .

Michael Karas