As reported by Insider Gaming, a Reddit user has leaked early-build screenshots of Call of Duty: Black Ops III's canceled open-world campaign, and they provide some interesting insight into what Treyarch had in mind. The leaker's profile is listed in the Insider Gaming article, however, this profile yields no connection to the leaks, so the source for the images is currently unknown. The entire list filled with dozens of screenshots can be found here.
It has been previously reported that the 2015 iteration of the Call of Duty series, Black Ops III, was originally planning an open-world campaign, which would have been a first for the series. This was reportedly worked on for about a year before being scrapped for a more traditional level-based linear campaign that's what's usual for Call of Duty (although it did feature co-op gameplay and more open level design).
These screenshots reveal some key bits of information about this scrapped campaign, such as the different sections of the world, the look and layouts of these sections, certain in-world game modes, and its day-and-night cycle. There would have been a 'Chinatown' area, a 'Downtown' area, a 'Hilltop' area, and a 'Black Station' area, according to the leaked images.
There were location-based survival modes, where you had to survive hordes of enemies in a round-based system, not unlike Call of Duty's famous Zombies mode, and there were also timed defense modes, where you had to protect cargo from enemies for a limited amount of time. It also seems that there was to be some level of environmental destructibility, as one screenshot showed a prompt for the player to bash some pillars in their way.
Call of Duty: Black Ops III was the twelfth entry in the series overall, and developer Treyarch's fourth Call of Duty game. It continues the now-prolific Black Ops subseries of games, which began with the original beloved classic Call of Duty: Black Ops in 2010, which many fans praised for its more psychological storyline that differed significantly from Call of Duty campaigns of the past. It seemed Treyarch wanted to change the mold again with Black Ops III but was unable to do so, likely due to time constraints.