Forum:Message when uploading images

I noticed that the [http://yugioh.wikia.com/wiki/Main_Page Yu-Gi-Oh! wikia], when uploading images, displays a message at the top of the page warning the users do not upload certain types of images. I'd like to do the same on another wiki, how do I do it? --Yuidirnt the Kevin 11 fan! 16:14, March 16, 2010 (UTC)