Phtcache.bin

File header:
00000-00007: Header 1UJQ00_1
00008-0000B: Number of pictures plus 1 (why?)
0000C-00011: Unknown static value : B8-0B-01-00-00-00
00012-00013: Total number of photos (excluding 2D dups)
00014-00017: Appears to be file size. It's only 32 bits = 4GB max. A few hundred K
                larger than the actual size of every file in DCIM (?)
                1607971 vs DCIM/100NIN = 1441792 vs DCIM = 147560 vs files = 1409024
                vs non-disk usage = 1224857
                phtcache non-disk = 456024, disk = 458752
                phtcache (non) + files (non) = 1680881 - 1607971 = 72910 = 72K hmm...
                maybe the 72910 is some kind of checksum?
                ( I have no clue, all these notes were probably worthless)

From 0x0018, one block per picture. Each block is 0x152 bytes long and formatted as such:
00000-00003: Preferred image file format. Should be MPO\x00, JPG\x00 or AVI\x00.
00004-0000B: Name of image
0000C-00013: Subfolder of image
00014-0001B: Time taken based on "DS epoch" (start of 1/1/2000) (UNIX+946684800)
0001C-00023: Time last viewed?
00024-00027: UNKNOWN 
00028-0002B: UNKNOWN
0002C-0002D: UNKNOWN
0002E-0002F: UNKNOWN
00030-0003F: UNKNOWN
00040-00043: File size

File Header

Name	Size	Description
Unknown	0x08	always 1UJQ00_1
Number of Pictures	0x04
Unknown	0x06	Always B8-0B-01-00-00-00
Total number of photos	0x02	excluding 2D dups
Unknown	0x06	File size ?
Pictures Property	0x152 * Number of Pictures	Index refereed by 3DS Camera

Pictures Property

Offset	Size	Description
Extension	0x04

Infos

The file seems to be guards against all external changes.