Filenames usually follow this pattern:
<subject_id>_<image_index>.JPG
Examples:
00013_00M19.JPG
00333_02F43.JPG
00654_04M62.JPG
Parsed fields:
subject_id: Person ID. The same person can appear in multiple images.
image_index: Image sequence index for one person.
gender: M or F.
age: Integer age value.
