Nin.com does not host any images or video. Instead, it imports images and video from your Flickr and YouTube accounts. To add images to nin.com, you'll first need to add those images to your Flickr account. Flickr membership is free, and the service is easy to use.

Make sure you have authenticated your Flickr account with nin.com. Do this by editing the "Contact Info" section of your profile, and following the instructions at the bottom of the page (view detailed instructions).
In the nin.com image galleries, use the pull-down menus at the top of the page to locate the gallery you wish to add photos to.
    
On the gallery's main page you'll see a Flickr code listed. Every gallery on nin.com has its own unique code. Copy that code, and add it as a tag to your image on Flickr. Any of your Flickr images tagged with that code will automatically display on nin.com in the corresponding gallery.
    
Usually images will appear on nin.com a few minutes after you tag them on Flickr, but sometimes it can take longer - even up to a day. Consult the FAQ if your images don't show up on nin.com after a while.

Still confused? View the step-by-step guide to adding images.