Monks,

Some time ago I accidentally erased a Compact Flash card with digicam images, before I copied them to another medium. Stupid...

Luckily I realised that those Flash Cards have some basic file system layout, very similar to ye olde FAT-16. This means that erasing a file just sets a bit in the allocation table instead of physically removing the data from the actual file blocks. Also, I was pretty sure that I didn't erase single images in between, so the actual image data would likely be aligned in consecutive file blocks.

I mounted the CF card on my Mac (using a PCMCIA adapter) and copied the file system to a disk image. After some tinkering with JPEG and EXIF file format specifications I was able to recover the images.

Now this is a real kludge, with the following limitations (at least):

• The whole disk image is read into memory (my CF card was only 8 MB - YMMV!)
• This only works if disk blocks are aligned, in other words, the disk image may not be fragmented
• You need to be able to dump the CF contents to a file; on Mac use Disc Copy (uncompressed!), on Un*x/Linux try something with dd(1)

Hopefully no-one will ever need this ;-)

#!/usr/bin/perl -w
use strict;
#
# Quick kludge to extract Digicam images from a file
# e.g. a disk image from an accidentally erased CF card
#
# Scan string for the folowing markers:
#   SOI - Start of Image = \xff\xd8
#   APP1 header for Exif = \xff\xe1
#   EOI - End of Image   = \xff\xd9
#
# Note that the whole blob is read in memory - YYMV!
#
die "$0 <file> with embedded EXIF images\n" unless (-f $ARGV[0]);
my @IMGS;
{
  open(FH, $ARGV[0]) or die $!;
  local $/ = undef;
  # Hmm... this breaks on embedded (EXIF) thumbnails...
  # @IMGS = split(/\xff\xd8/, <FH>);
  # For EXIF only:
  @IMGS = split(/\xff\xd8\xff\xe1/, <FH>);
}
# 1st array element contains leading crap
for my $idx (1..@IMGS-1) {
  open(FH, sprintf("> img%02d.jpg", $idx)) or die $!;
  # cut crap after EOI marker
  print FH "\xff\xd8\xff\xe1", split(/\xff\xd9/, $IMGS[$idx], 1), "\xf
+f\xd9";
  close FH;
}
[download]

--
Cheers, Joe

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