As far as guessing scores from pictures, they did a contest on Monster Muleys for a while where people guessed the score of deer that had been officially scored. Generally there were several pictures of each deer so people would have the ability to really make a good guess. I actually was the one that did the math on the guesses in an excel spreadsheet for them to keep track of who won each contest. We did 13 different contests and out of the 193 people that entered 10 or more of the contests the average guess was off by 10.74". The winner of the contest was off by 7.29" on average but the way we did the contest we threw out the worst 3 guesses. The winner had one deer that they misjudged by 26.125". Out of the 193 people in the contest the average of their worst guess was 24.599" off.
I would say that guessing the score of a deer from a picture isn't an exact science but it works well for some deer. The guy that won the contest had 4 deer that he guessed to within an inch or less. Some can be deceiving though.