Which of the following $4$ statements is correct?

a$.$ The header of a graphics file is not a part of the picture data and thus plays no role in producing the picture for the purpose of presenting the evidence.

b$.$ Each type of graphics files has a unique header containing information that distinguishes it from other types of graphics files.

c$.$ If being damaged, the header of a graphics file cannot be recovered.

d$.$ All graphics files use the same unique header containing information that distinguishes them from other types of files.