First upload the image to the site and wait for it to be approved. Upload the image as a "Caricature" (if it's you as a Simpsons character) or "Misc. Images" (if it's something else).

Once the image has been approved, it will appear in your "My Images" page, and you'll receive an email with a link to it. Click on the "My Images" link below 'Your Account:' and check for it there (or use the link from the email).

The URL for the image will appear below it, something like this:
URL for this image: http://www.simpsonscollectors.com/images/customs/2/eh_back_finished.jpg

Copy the URL or right-click on the link and select "Copy Shortcut". Please make sure to include the "http://" portion of the URL!

Now go to your EZ Board control center and go into the "Edit Profile" page. Paste the URL of your image into the box where it says: "Personal Photo URL" and check the box that says "Use Personal Photo".

If you have more questions, refer to the FAQ answer about adding a Personal Photo.