I'm using the version 0.33 of Mediawiki::API. So i need to upgrade it?
yes. 0.33 was released two years ago, before the mediawiki API had support for file uploads (1.16 which had this support was released a month or two after). 0.39 is on cpan.
http://search.cpan.org/~exobuzz/MediaWiki-API-0.39/
Best Regards
Jools