To add art to an entry, you first need to upload the image to the page to which you want to add it. You can do this via the "files" button at the bottom of each page. Examples of wiki code that can subsequently be used to add images to the wiki can be found here.
Please upload the images at a reasonable image size, and preferably use jpg files. While the 300 MB file storage limit of Wikidot.Com wikis might seem large, it could fill up quickly if many artists contribute to it.
Finally, when you add an image to the wiki, also provide a link to the original source of the image (such as a gallery). Do not upload images unless you can prove that you are either the creator of the image or that the image is in the public domain - the link must be added to prove just that, and images without such proof will be purged from the wiki.