Originally Posted by Jaapjan
Well, the FCIS I know because it contains a field with the content length as well as a field that indicates the number of images available in the file. It also grows and shrinks depending on how many image files are present in the file so it suggests it is something of an information record where most information is for the images.
OK. But this record is not obligatory. Maybe it is some kind of optimization.
Which record is cover image and which is thumb nail is given by data in EXTH.