Pictures can be insert so that they are 'floating' in the graphics layer, if
they aren't anchored so that text flows around them. Pictures can be
inserted in-line so that they act like a character and move when the
character next to them moves. If the print option to print graphics isn't
set, then you won't see those floating pictures in the graphics layer in
print preview. Also since floating pictures float, they move around and
might not be where you left them before adding other things to your
document. Also depending on how you linked the picture to its file path, if
you move or delete the original picture in the file system, then word can't
find it to display. You usually want to use the save with document option in
the insert picture dialog and uncheck link to file, unless it is something
like a picture of a chart, whose name won't change, but its appearance might
change.