This should help understand jpeg headers.
Warning: I don't understand the jpeg headers or jpegs that well!
Oh well, I will try to explain here anyway.

Jpeg markers in general:
------------
0xFF marker# lenth(2 bytes) data
length is the size of the information after the 0xFF XX

Quantization tables:
-------------------
0xFF 0xDB 0x00 length tables
Funny.....for what I have the data is all 0x01's.
I guess there is a precision number in there somewhere, but I don't know.
For what I have, both quantization tables are precision 0.
Precision 1 will not be used by us. We need precision 0.
Jpeg's have two tables. 
Table 0 should be luminance and table 1 should be chrominance.

Start of Frame 0:
----------------
0xFF 0xC0 0x00 length bits-per-pixel 0x00 height(2 bytes) width(2 bytes)
  #_of_components sets(1 or 3 of them)
A set would be component# v/h quantization-table-number.
The v/h is the vertical to horizontal compression ratio.
I misplaced some info I had on the components here.
There are a couple of formats that the data could be in.
The 3 component ones are YCbCr and CMY.
The 4 component ones are YCbCrK and CMYK.
The #_of_components is set to 3 or 4 accordingly.
The component# can be something like 0 through 5
The component# would refer to Y, Cb, Cr, C, M, or K
1=Y, 2=Cb, 3=Cr, but I forget what C, M and K are.

Huffman tables:
--------------
0xFF 0xC4 0x00 length ACorDC bits(16 bytes) Huffman_values
length is the size of that huffman table (you don't count the FFCO)
Repeat until length is exhausted (usually 4 Huffman tables):
	If ACorDC>=0x10 it is an AC table, otherwise, it is a DC table
	The length of the Huffman_values is the sum of the previous 16 bytes

Ending piece of header (I have no clue what to call it):
-------------------------------------------------------
0xFF 0xDA length(2 bytes) #_of_components(1 byte) sets Ss Se Ah Al
Ss and Se, I guess are each one byte.
I guess Ah and Al are one byte total.
The sets are: component#(1 byte) DC+ACtable#'s
For DC+ACtable#'s, the high nibble is DC table# and the low nibble is AC table#

        # Quantization tables given in JPEG spec, section K.1

        # This is table 0 (the luminance table):
          16  11  10  16  24  40  51  61
          12  12  14  19  26  58  60  55
          14  13  16  24  40  57  69  56
          14  17  22  29  51  87  80  62
          18  22  37  56  68 109 103  77
          24  35  55  64  81 104 113  92
          49  64  78  87 103 121 120 101
          72  92  95  98 112 100 103  99

        # This is table 1 (the chrominance table):
          17  18  24  47  99  99  99  99
          18  21  26  66  99  99  99  99
          24  26  56  99  99  99  99  99
          47  66  99  99  99  99  99  99
          99  99  99  99  99  99  99  99
          99  99  99  99  99  99  99  99
          99  99  99  99  99  99  99  99
          99  99  99  99  99  99  99  99

Those are not in the order that it appears in the jpeg.
Those two tables are accessed in this order:
	   1   3   4  10  11  21  22  36
	   2   5   9  12  20  23  35  37
	   6   8  13  19  24  34  38  49
	   7  14  18  25  33  39  48  50
	  15  17  26  32  40  47  51  58
	  16  27  31  41  46  52  57  59
	  28  30  42  45  53  56  60  63
	  29  43  44  54  55  61  62  64

Comparing the before and after of putting a really high and out of place number
in the table will help you locate bad spots in the table. It will make an
obvious distortion in the image. Use this technique to find the table entry 
that affects the pixels that are distorted and then decrease the difference
between that table entry and the ones around it (look at the order table).

The greater the difference between the numbers in the table, the greater the 
contrast or annoying shadow. Smaller differences will create smoother 
transitions between pixels. A table entry of 0 will make the table result be 0.
Consider the quantization table as a multiplier table. For every dot in every 
8x8 block of the picture, the input is multiplied by the corresponding value in
the quantization table. Therefore, you can probably find out what quantization 
table entry needs to be changed by looking at its coordinates. Keep in mind 
that different compression ratios are used for different cameras though, so 
this might not work the same way for all cameras. If you use a bunch of 1's in
the tables, you will probably come up with a very dull image.
