Head on over to the UnMario Wikia. Be sure to register an account if you haven't already.

From Unmariowiki

Use the form below to upload new files, to view or search previously uploaded images go to the list of uploaded files, uploads and deletions are also logged in the project log.
You must also check the box affirming that you are not violating any copyrights by uploading the file. Press the "Upload" button to finish the upload.
To include the image in a page, use a link in the form [[{{ns:6}}:file.jpg]], [[{{ns:6}}:file.png|alt text]] or [[{{ns:-2}}:file.ogg]] for directly linking to the file.

Before you upload, ask yourself "Does this image really need an upload?". Avoid personal images and animated GIFs.