Use whatever image hosting service you like and post the link to /r/woodworking. The key here is it needs to be apparent that you've built the entry, and you follow the photo requirements listed in the contest rules. Submissions of finished photos only will not be accepted for entry. <-- I can't emphasize this enough, you absolutely need more than 2-3 photos for a valid submission. I will no longer accept entries that have albums that go from rough stock to 90% complete in one jump.
Typically furniture such as tables and chairs is made using solid stock from hardwoods due to its strength and resistance to warping. Additionally, they also have a greater variety of grain patterns and color and take a finish better which allows the woodworker to exercise a great deal of artistic liberty. Hardwoods can be cut more cleanly and leave less residue on sawblades and other woodworking tools. Cabinet/fixture makers employ the use of plywood and other man made panel products. Some furniture, such as the Windsor chair involve green woodworking, shaping with wood while it contains its natural moisture prior to drying.