DVOA has posted the photo O, with answers.

This race was interesting, given that I found 15 of the controls, but only figured out 2 from the photos before going out.

I saw #216 on the drive in, Vadim told me there was one at #203, and I figured there would be one at #201, as that building was visible from the pavilion, and I would have put one there. #201 was confirmed by the group that started before me.

The rules prevented carrying the photos with you, so you either had to find the feature on the map, memorize the photos, come back to the pavilion during the race, or something else, like just run around to various features looking for bags. There was 60 minutes total time between studying the photos and going out to look for the bags. I decided on a combination of the above strategies.

After about 2 minutes of photo study, I had only located #212 and #220. After 3 minutes, I still had not figured any more out. After 3:28, I decided I was wasting enough time, figured I had the pictures memorized, and decided to go out hoping for the best. I figured there would be overlap between the beginner's course and the photo O, so if I could find that and get on it, I'd be set.

I went to #201, then wandered around the woods in that area, no luck. I decided speculating on features deep in the forest was a losing strategy. I got on the trail network deciding to go to the known #220, and hit #217 by luck. I decided to go to #212, from #220, speculating on various buildings on the way, no luck, but saw people leaving with purpose from #212. Used them to get to #218.

Ran randomly on the trail network, saw Hunter running with purpose, used him to locate #213, along with memory of that photo. Saw another runner running towards the lake, used him for #214.

Knew I was on the beginner course when I found #223 (not part of the photo O), and stayed in the "white course terrain" to find #211 and #209. Knew one was on a stone wall, and speculated to find #205. Stayed on the trail to hit #204. Was going to speculate on the feature #208, but saw activity in the fields, and went with others who were speculating, but found nothing. Missed #208 because of this. Picked up #203 on the way back to the pavilion for more study.

Still could not figure out any of the photos remaining; decided to speculate on the boulders and campground to the south, and picked up #215. Picked up the known #216, and went into the forest speculating on rootstocks.

No luck, so headed back to the pavilion again; lots of activity in the woods got me #202. Went out for another foray into the south, and could not find anything.

So, my breakdown was 3 a priori knowledge, 2 from photos, 4 using others, 1 on speculation, and 5 on luck. It would have been nice to do it more honestly. Assuming I could have kept up my rate of 2 controls per 3.5 minutes of puzzling, a half hour of puzzling should have located them all. Then, they could all have been picked up in the remaining half hour. Problem was, I did not feel I could force success on puzzling them all out under the pressure of the clock. Also, I didn't do this sort of analysis on the clock either. In any case, fun event, I think more fun if 90 or 75 minutes were allowed.