We bought a 2003 Toyota Sienna with 50k miles on it. We've had it for about six years and it now has 108k miles. It has never used much oil until about 6 months ago. I probably went longer than I should have between oil changes (don't ask me how long; I have no idea) and when I checked the oil one day it was probably at least 3 quarts low. Ever since then it has been burning about a quart of oil every 400-600 miles. It usually smokes out the exhaust on startup, especially after sitting for a while. I've had one mechanic tell me I need a new engine but all he did to diagnose it was start it up and watch it smoke. I changed the spark plugs this weekend and I've attached a picture of what I found. Is there any way to determine whether the problem is rings, valve guide seals, or both? Is there any hope for my engine or did I destroy it?