An observation on the photo in #8. That sniper is using an Anti-Reflective Device on the objective. That's outstanding.
To your question, his scope may be equipped with a mil-dot reticle (mil = milliradian),which would allow him to estimate distance. The Marine Corp really did good with this innovative idea in the 70's? and the other services have caught on and now use them.
Mil-dots are either etched on glass or comprised of wire. They used to be made for use at 10X , but now companies are providing mil-dots that are usable and allow the mil spacing to remain constant throughout the range of a variable power scope.
Army spec mil-dots have posts that are ~40% narrower than the posts used by the Marines. The common 3/4 minute mil-dot is just that - the dot mass is 3/4 minute of angle. Actually for the oval mil-dot, the dot is slightly longer and and narrower that 3/4 minute, BUT the dot length is 1/4 mil.
Mil-dots are used on both weapon scopes and also spotting scopes. You can buy products (e.g. Mil-Dot Master) that allows you to compute a firing solution very quickly. It's basically a slide card that allows you to move an inside card based on data you collect (considerations of knowing the size of various objects (e.g. road signs, standard piece of plywood, etc and also how many mil-dots does the object take up in your scope . Knowing that 1 minute of angle (MOA) at 100 yards is 1.047" (or ~1") and also 1 mil = 3.438 MOA allows these types of devices to be easily used. Of course, they offer the calculations in meters as well.
You should also know the ballistics of the particular round you are shooting. For example, several companies that do mil-dot modifications have ballistic info on the Federal Gold Medal Match .308 168 and also 175 grain round. The military also has the ballistics info for the round they use.
That shot is very, very good. He was probably contending with wind velocities and directions that varied quite a bit from his position downrange to the target. If you wanted a 1 MOA dot on the target at 800 feet, that would give you around ~8" to work with - not much. This guy's shot was at ~850 meters - that's good shooting.