The snake that bites Thomas (at 0:18:48 in the 3:02:00 version) has a brown body with extremely irregular longitudinal yellow stripes or streaks that no grass snake has.
The photo that is taken of the boy by Gregor Lämmle (and shown in black/white) does not match the photo later on in the movie. The first picture is taken (at 1:25:21 in the 3:01:40 version) straight towards the boy; the second picture is taken (at 1:56:53) from a slight angle to the left (15% or so). (There is another difference: the first image is shown while the picture is still an undeveloped negative on the film in the camera. This first image is of Thomas as we, not the camera, see him but in black and white while the picture is being taken - we would not be between Thomas and the camera, so the angle at which we see Thomas would be different than how the camera sees him.)
A 50-star American flag is shown flying in New York City (at 1:11:51 in the 3:02:00 version).
When Maria and Thomas are climbing the mountain, you can clearly see their shoes. They appear to be modern 21st century shoes, they're definitely not from WW2.