basically, dynamic content is generated based on certain parameters (eg. this topic is changeable from users perspective because after you post a reply this page includes your post ... on the other hand static html pages have content set by the creator and other viewers with non-admin access can not change it) ... so dynamic content can be changed by user who can submit code (eg. script - which is not allowed here) that could execute malicious software, access to personal data or simple crash of the site
so simply, there is a good reason for the current setup and images can be inserted to posts in other
btw, the particular image you mentioned at the beginning includes "&" in its title which is used in address of dynamically generated pages (including parameters in the address - as the address of this post http://brainden.com/forum/index.php?showto...mp;#entry45772) - and security of this board did not identify it as a simple image