SLAMorris Final Thesis After Corrections.pdf - Cranfield University

5.9.1 Metadata
There are three distinct types of metadata contained within a subrecord: the
URI of the original source file, information on the original source file, and
information about the visual thumbnail. The information about the visual
thumbnail can assist in checking if the image is reliable, and can also be used in
conjunction with the techniques discussed in Section 5.9.2 to identify visual
thumbnails which are the same. The information within the subrecord relating to
the original source file can assist with forming a relationship as it can be used to
check the source file has the same properties. Finally the URI can assist with
forming a relationship as it provides a location in the directory structure for the
original source file. The filename of the subrecord is an MD5 hash of the URI,
which can be used to corroborate a relationship between the subrecord and the
original source file. Checking the source file’s URI along with the metadata
stored in the subrecord about the original file can provide a stronger relationship
between the file and the subrecord, if the two sources of metadata agree.
5.9.2 Images
Each file type which is eligible for visual thumbnail generation uses a specific
algorithm; the generation algorithms and the list of associated file types is open
source. Therefore it is possible upon knowing the file type of the original source
file to use the appropriate algorithm, which would create a visual thumbnail. The
IDAT chunks of the created thumbnail can be compared with IDAT chunks from
existing subrecords to identify any matches. Finding a subrecord with a
matching image does not show that there is a relationship between the original
source file and the subrecord, as multiple copies of a file may exist. It is also
possible that the subrecord was created earlier in the source files event timeline
and does not accurately reflect its current status; for example, it may not be at
the correct URI.
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