Didn't know about PhotoRec, so I wrote my own jpeg data recovery script in April 2008.

filenose.py

#!/bin/env python
# filenose - Find specific types of files from raw data.

from StringIO import StringIO
import sys
import time
from datetime import datetime

MAXSIZE = 1024*1024*4 # 4mb
CHUNK_SIZE = 1024*1024*10 # 10mb

filetypes = {} # (start, end) hex symbols for each file type

filetypes['PHOTO.JPEG'] = ('\xff\xd8\xff', '\xff\xd9')
# ffe1 is exif
# ffe0 is application marker

def find_jpeg_photo(fp):
    START, END = filetypes['PHOTO.JPEG']

    data = fp.read(MAXSIZE)
    if not data:
        raise TypeError("end of JPEG not found before EOF")
    
    if not data.startswith(START):
        raise TypeError("start of JPEG not found")
    
    if data.count(END) < 2:
        raise TypeError("end of JPEG not found within MAXSIZE")
    
    # Find second occurance
    first = data.find(END)
    second = data.find(END, first+1)
    
    data = data[:second+len(END)]
    
    if 'Canon PowerShot SD850 IS' not in data[:first]:
        raise TypeError("important string not found in data.")
    
    # Success
    return data

def search_device(fp):
    "Read CHUNK_SIZe at a time, looking for key markers. Once found, extract file."
    # TODO: Make a generic version of this to look for all types
    
    LOOK_FOR = filetypes['PHOTO.JPEG'][0]
    
    count = 0
    iterations = 0
    last_progress = fp.tell()
    last_progress_time = time.time()

    while 1:
        iterations += 1
        last_pos = fp.tell()
        if (iterations % 1000)==0:
            now = time.time()
            sys.stderr.write("Progress %s: %d (%.2f mb, diff: %.2f mb/sec)\n" % (datetime.now(), last_pos, (last_pos/1024.0/1024.0), ((last_pos-last_progress)/(1024.0*1024.0)/(now-last_progress_time))))
            sys.stderr.flush()
            last_progress = last_pos
            last_progress_time = now
        chunk = fp.read(CHUNK_SIZE)
        if not chunk:
            print "Done!"
            break
        loc = chunk.find(LOOK_FOR)
        if loc >= 0:
            seek_to = fp.tell()-len(chunk)+loc
            # print "Seeking to: %d" % seek_to
            fp.seek(seek_to)
            found_at = fp.tell()
            try:
                # print "Candidate found at %d, checking..." % fp.tell()
                data = find_jpeg_photo(fp)
            except TypeError, e:
                # print "Candidate eliminated: %r" % e
                rewind_to = found_at + len(LOOK_FOR)
                #print "Rewinding to %d and continuing search..." % rewind_to
                fp.seek(rewind_to)
                continue
            save_path = "%0.4d.PHOTO.JPEG" % count
            print "Candidate successful at %d! Saving to: %s" % (found_at, save_path)
            sys.stderr.write("Match found at %d\n" % found_at)
            fp_candidate = open(save_path, 'wb')
            fp_candidate.write(data)
            fp_candidate.close()
            count += 1

if __name__ == "__main__":
    path = sys.argv[1]
    print "Searching device: %s" % path
    fp = open(path, 'rb')

    if len(sys.argv) > 2:
        seek_to = int(sys.argv[2])
        print "Seeking to: %d" % seek_to
        fp.seek(seek_to)

    search_device(fp)