Apache 2: Negative FilesMatch / FilesNotMatch
Sadly there doesn't seem to be a way to negate a file match in Apache.
However, the regular expression library that Apache uses is PCRE (Perl Compatible Regular Expressions). This means you have the full power of Perl's regexes, including their negative lookbehind and lookahead assertions. These are fairly complicated and powerful features. I can't be certain that this will work, especially without knowing the full layout of your images, but you might be able to use something like:
<FilesMatch "(?<!ban).*\.(gif|jpg|jpeg|png|mpg|avi)$">
Almost correct - you need to use \b(?!.*ban.*)(.+)\.(gif|jpg|jpeg|png|mpg|avi)$
regexp for such exception.