The site doesn't have specific capabilities for uploading pictures to it at this time. You have to use an outside host, such as photobucket.com. It is completely free to sign up.
For a complete tutorial on how to use put the picture here from the outside host, see JohnB's guide:
2007 T-286SR Cherry/Granola, #6236, original owner, current mileage: 9467.8 (as of 5/26/19)
1997 T-2653 Blue Denim, #5471
1979 12 1/2' MC, Beige & Avocado, #4639
Past Sunlines: '97 T-2653 #5089, '94 T-2251, '86 T-1550, '94 T-2363, '98 T-270SR