A reverse google image search suggests that the second image is from a British field hospital during the Battle of Epehy in September 1918. In other words, a captured German.

Nothing substantive on the second image, but I'm note entirely convinced those men in german helmets are actually German, as opposed to men of the same unit posing with captured helmets.

edit: as I suspected, despite many attributions to the first image being from the Christmas truce, this website which seems more reliable than the other citations, describes it as Canadians returning from the battle of Courcelette. In other words, same unit with captured helmets.