We will be having the cover and mascot contest again this year, similar to last year. It will be announced and started around April. It will end in July or August. We might end it a little earlier this year (July) to give more time to integrate the new mascot art, colors, and design into the web site so it can go up quickly after the con (rather than at elections like last time).
Also, there is a possibility we will have a theme rather than being wide open, although it hasn't been decided yet. The reason I point this out, is that interested participants shouldn't begin yet--we don't want anyone to spend a lot of time working on something before the contest has been announced and then find it doesn't qualify.
As for not allowing publishing the entry anywhere else before the contest is over--this might disqualify too many good possibilities, if the entrant has perhaps posted it casually or distributed it a little bit to friends. One possibility is to just not allow linking to it on the forum, but not have a blanket rule against having ever publicized it elsewhere (I think this is how Sakura-Con does it). We're still thinking about how to handle this.