I don't think those photos are staged, you can see people firing and bodies, I don't think it would have gone down well to stage it, plus as said they didn't use blanks. They're great photos, the first confirmed photos of combat, i hope to recreate those scenes eventually.
image of fighting during the battle of Sedan, franco-prussian war. here you can see prussian lines drawn up and firing with many dead and wounded around. this type of warfare was still around at the time and it wasn't until 1884 that Hiram Maxim's new invention was introduced. breach loading weapons of better quality continued to be developed through this last half of the century and also artillery was further developed as these new rifles now had greater range then the canister fire range of canons so better use of howitzers began to develop with there range and accuracy increasing each time.
the franco prussian war was the last major war between two european powers until WW1 which by then no one had any real experience with the new inventions leading to old age tactics being used and the slaughter that followed.
I don't think linebattles will be possible in this mod.. rifles already had very long range and a fast reload (but still single-shot) around this time. Artillery will be even more powerful, if Willhelm has success making the mitrailleuse this will make the things drastically different. This will develop the creation of player-made cover in open field maps.
I've already begun adding more cover to the default maps, i think line battles will be possible to an extent but regiments will have to use skirmish formations and get behind cover, It won't be too unfamiliar to napoleonic wars and i think skirmisher regiments will feel at home, forming a line in combat would be suicide though, just playing with the bots in custom battle, a volley in NWs that would take out 3 or 4 men takes out 15.
This is the accuracy of the Chassepot and Dreyse without bayonets in the hands of regular line infantry.