It's up to the community to upload them, but we've got the functionality built into the site and it's ready to go. Check out the FAQs for more info, we'll have this better documented shortly.
Another big update today: registered users now have access to a flagging feature. If you are logged in and find bad or offensive content you can flag it and help us focus on rolling out more features. Log in when you browse the site and you'll have this tool available to you underneath the "Add a Comment" section. Feel free to flag those Flash Miis as more Wiis become available, non-Mii pictures or broken pictures. It takes a small percentage of the installed user base to remove the content, so please help us out by staying active and thinking carefully before flagging content. We've also started expanding on information about users, and hope to have more soon.