The human footprints were mine. My footprints looked surprisingly narrow compared to when I look down at my bare feet and they look so spread out. The inspiration for the footprints was because I bought a used book called Barefoot Running by Michael Sandler.
Altogether, I tried barefoot walking for short distances 3 different times on FR181/American Springs Road. I carried my shoes while doing that. FR181 has a lot of small pebbles that painfully drill into my feet unless I'm careful. On the smoother stretches, walking barefoot felt good. Admittedly, I was taking only careful, tiny mincing steps - hardly a normal gait.
In 2008, I tried the Nike Free shoes and they probably led to the stress reaction in my right heel. This is most likely because I pounded my heel hard on rocky trails on my walks and the Nike Free shoes gave it little protection in comparison to the shoes I was used to wearing. Now, in reading Sandler's book, I realize that it's better to land on the forefoot first to take pressure off the heel when barefoot walking or even when wearing minimalist shoes.
One obstacle I see in colder weather is that even though my feet didn't feel cold while I was barefoot on the dirt road, the cold must have seeped up into my body because it took a long while to warm up after walking.
All in all, I'd probably feel safer (and warmer) with some kind of minimal shoes (and socks in the winter!) I'm afraid of stepping on sharp things, man made or natural. From my brief experience today, though, I can see that barefoot walking is best done in a truly unshod state (as opposed to barefoot mimetics utilizing minimalist footwear) because anything on the bottom of the foot means you can't feel the ground as well and this interferes with the natural movement.
Anyway, unfortunately, I have too much feet pathology to seriously make a regular diet of barefoot walking - chronic posterior tibial tendon dysfunction, flat feet and a heel spur (that flared into a stress reaction and painful plantar fasciitis in 2008) - but perhaps I could try stints here and there to strengthen my feet.