Make it on MS Paint, Fresco, Paint.NET or whatever and save it as a .jpg or .jpeg
There's an imageshack uploader on the "reply" section but it's not worked recently... so go to www.imageshack.us
Click Browse, select your pic and click upload.
On the "Done" screen, go down until you find the code for "Forums 1", copy and paste that into here and click post. Jobs a good un.