From ModMyiFone - Wiki
Step 1
Download iThmbConv.exe from here.
There are also a couple files that you need to download off of your iPhone before you can convert them. Use a program like iPhoneBrowser or iBrickr.
The files are:
Photo Database
F3004_1.ithmb
F3008_1.ithmb
F3009_1.ithmb
F3011_1.ithmb
They are located at:
/var/root/Media/Photos/
and
/var/root/Media/Photos/Thumbs
Step 2
Copy all five files and the program to:
C:\tmp
(Note: the directory is not important, but this is for simplicity.)
Step 3
Click Start > Run.
Type "cmd" and hit enter.
This will bring up the command prompt.
Step 4
Now you need to navigate to the folder that you downloaded the five files at.
Type "cd c:\tmp" and hit enter.
Step 5
Now type "iThmbConv.exe"
There will be a list of examples on how to use the program.
Step 6
Type "iThmbConv c:\tmp\F3008_1.ithmb" and hit enter.
Note: be sure that this file is the largest one you downloaded, if it isn't, choose the one that is.
Step 7
You will now have a bunch of files in your tmp directory that have a .ppm extension.
You can open these files using Photoshop and save them as you want.
You could even use a batch to convert them all at one time.