title: Extract thumbnail from jpeg file
body: <p>I'd like to extract thumbnail image from jpegs, without any external library. I mean this is not too difficult, because I need to know where the thumbnail starts, and ends in the file, and simply cut it. I study many documentation ( ie.: <a href="http://www.media.mit.edu/pia/Research/deepview/exif.html" rel="noreferrer">http://www.media.mit.edu/pia/Research/deepview/exif.html</a> ), and try to analyze jpegs, but not everything clear. I tried to track step by step the bytes, but in the deep I confused. Is there any good documentation, or readable source code to extract the info about thumbnail start and end position within a jpeg file?</p>
  
  <p>Thank you!</p>