原文出處：　http://motherboard.vice.com/read/hack-this-extra-image-metadata-using-python

1) ExifRead　
利用python 函式庫　ExifRead　即可輕易地作 tiff/jpeg 檔案格式的元數據metadata抽取
先透過PIP安裝好ExifRead函式庫　
$pip install exifread

直接在CLI命令列執行　EXIF.py，即可對單一照片檔案image1.jpg　來抓出此張照片相關資料數據
$ EXIF.py image1.jpg
我以自己一年多前利用手機拍的這張照片為例
利用ＥxifＲead函式庫執行上一行指令，傳回來的結果如下：

Opening: pic.jpg
EXIF ApertureValue (Ratio): 2
EXIF ColorSpace (Short): sRGB
EXIF ComponentsConfiguration (Undefined): YCbCr
EXIF DateTimeDigitized (ASCII): 2002:12:08 12:00:00
EXIF DateTimeOriginal (ASCII): 2015:06:13 10:21:45
EXIF ExifImageLength (Long): 2448
EXIF ExifImageWidth (Long): 3264
EXIF ExifVersion (Undefined): 0220
EXIF ExposureTime (Ratio): 11/20000
EXIF FlashPixVersion (Undefined): 0100
EXIF FocalLength (Ratio): 177/50
EXIF ISOSpeedRatings (Short): 100
EXIF InteroperabilityOffset (Long): 535
EXIF UserComment (Undefined): d with VSCOcam
Image Copyright (ASCII): COPYRIGHT 2015. ALL RIGHTS RESERVED
Image ExifOffset (Long): 275
Image GPSInfo (Long): 565
Image ImageDescription (ASCII): Processed with VSCOcam
Image Make (ASCII): Xiaomi
Image Model (ASCII): MiTwo
Image ResolutionUnit (Short): Pixels/Inch
Image Software (ASCII): VSCOcam Android Version: v3.3.2 (217)
Image XResolution (Ratio): 72
Image YCbCrPositioning (Short): Centered
Image YResolution (Ratio): 72
Interoperability InteroperabilityIndex (ASCII): R98
Interoperability InteroperabilityVersion (Undefined): [48, 49, 48, 48]
Thumbnail XResolution (Ratio): 72
Thumbnail YResolution (Ratio): 72

試了另一張別人拍的照片，其中最大的差異應該是拍照者有開啟手機的ＧＰＳ定位，故在其照片的元數據標誌上出現了地理位置的資訊。

File has JPEG thumbnail
EXIF ApertureValue (Ratio): 4845/1918
EXIF BrightnessValue (Signed Ratio): 14515/1629
EXIF ColorSpace (Short): sRGB
EXIF ComponentsConfiguration (Undefined): YCbCr
EXIF DateTimeDigitized (ASCII): 2013:03:09 16:36:20
EXIF DateTimeOriginal (ASCII): 2013:03:09 16:36:20
EXIF ExifImageLength (Long): 2448
EXIF ExifImageWidth (Long): 3264
EXIF ExifVersion (Undefined): 0221
EXIF ExposureMode (Short): Auto Exposure
EXIF ExposureProgram (Short): Program Normal
EXIF ExposureTime (Ratio): 1/1227
EXIF FNumber (Ratio): 12/5
EXIF Flash (Short): Flash did not fire, compulsory flash mode
EXIF FlashPixVersion (Undefined): 0100
EXIF FocalLength (Ratio): 107/25
EXIF FocalLengthIn35mmFilm (Short): 35
EXIF ISOSpeedRatings (Short): 50
EXIF MeteringMode (Short): Pattern
EXIF SceneCaptureType (Short): Standard
EXIF SensingMethod (Short): One-chip color area
EXIF ShutterSpeedValue (Signed Ratio): 10343/1008
EXIF SubjectArea (Short): [1631, 1223, 881, 881]
EXIF WhiteBalance (Short): Auto
GPS GPSAltitude (Ratio): 34
GPS GPSAltitudeRef (Byte): 0
GPS GPSImgDirection (Ratio): 23341/197
GPS GPSImgDirectionRef (ASCII): T
GPS GPSLatitude (Ratio): [22, 1002/25, 0]
GPS GPSLatitudeRef (ASCII): N
GPS GPSLongitude (Ratio): [120, 1833/100, 0]
GPS GPSLongitudeRef (ASCII): E
GPS GPSTimeStamp (Ratio): [8, 36, 41/2]
Image DateTime (ASCII): 2013:03:09 16:36:20
Image ExifOffset (Long): 204
Image GPSInfo (Long): 594
Image Make (ASCII): Apple
Image Model (ASCII): iPhone 4S
Image Orientation (Short): Horizontal (normal)
Image ResolutionUnit (Short): Pixels/Inch
Image Software (ASCII): 6.1.2
Image XResolution (Ratio): 72
Image YCbCrPositioning (Short): Centered
Image YResolution (Ratio): 72
Thumbnail Compression (Short): JPEG (old-style)
Thumbnail JPEGInterchangeFormat (Long): 890
Thumbnail JPEGInterchangeFormatLength (Long): 11733
Thumbnail ResolutionUnit (Short): Pixels/Inch
Thumbnail XResolution (Ratio): 72
Thumbnail YResolution (Ratio): 72

當然除了在ＣＬＩ執行EXIF.py外，也可以另外寫一支簡單python的程式碼，引入ExifRead函式庫，以善用其相關method功能。其中.process_file()的功能據稍是：to deal with all the arbitrary nasty bits　of the EXIF standard,什麼意思，我也不太懂，而其回傳的傳是一組dictionary的資料結構。



2) Pillow 另一個python 函式庫
之前習作過利用pillow (Python Images Library)進行圖片編修，而這回則是要利用它的
同樣也是先透過PIP 把它安裝好
$pip install pillow

TAGS, GPSTAGS 這兩個類別class的使用文件
http://pillow.readthedocs.io/en/latest/reference/ExifTags.html?highlight=ＴＡＧＳ
http://pillow.readthedocs.io/en/latest/reference/ExifTags.html?highlight=GPSTAGS
但其實寫了跟沒寫差不多，　請參考其原始碼內容，以了解這個dictionary各自key/value 之意義
https://github.com/python-pillow/Pillow/blob/master/PIL/ExifTags.py

照著原作，打入以下的程式碼,會回傳下面的key/ value 對應資訊

ExifVersion b'0221'
ComponentsConfiguration b'\x01\x02\x03\x00'
ApertureValue (4845, 1918)
DateTimeOriginal 2013:03:09 16:36:20
DateTimeDigitized 2013:03:09 16:36:20
FocalLengthIn35mmFilm 35
FlashPixVersion b'0100'
MeteringMode 5
Flash 16
FocalLength (107, 25)
ExposureMode 0
Make Apple
Model iPhone 4S
Orientation 1
YCbCrPositioning 1
SubjectLocation (1631, 1223, 881, 881)
SensingMethod 2
XResolution (72, 1)
YResolution (72, 1)
ExposureTime (1, 1227)
ExifImageHeight 2448
ExposureProgram 2
ColorSpace 1
GPSInfo {16: 'T', 1: 'N', 2: ((22, 1), (4008, 100), (0, 1)), 3: 'E', 4: ((120, 1), (1833, 100), (0, 1)), 5: 0, 6: (34, 1), 7: ((8, 1), (36, 1), (2050, 100)), 17: (23341, 197)}
ISOSpeedRatings 50
ResolutionUnit 2
ExifOffset 204
WhiteBalance 0
SceneCaptureType 0
FNumber (12, 5)
Software 6.1.2
DateTime 2013:03:09 16:36:20
ExifImageWidth 3264

試著再一行行拆解上面這簡單幾行的程式碼
from PIL import Image
from PIL.ExifTags import TAGS, GPSTAGS
img = Image.open("pic1.jpg")
print(img)
#螢幕回傳以下資訊：
info = img._getexif()　
print info
#回傳一組dictionary, 但其key以數字代表，從相應的數值value有些可以猜出它可能代表的東西或標記。如果用下面迴圈的寫法，得出來的內容物一樣，但不是dictionary型態，而是把dictionary每一個對應的key/value一一回傳打印出來。不過還是不知道變數"tag"代表的意義，這裏它仍只是一堆數字標誌的代號。
for tag, value in info.items():
print(tag, value)
另外再試這樣：
for tag, value in info.items():
print(TAGS.get(tag)
這次回傳印出的果然就是tag代表的標記數字意義
所以我把原文中的程式碼改成：
for tag, value in info.items():
key =TAGS.get(tag)
print(key, value)

透過這次練習，除了學到PIL.ExifTags模組以及ExifRead函式庫。其中又透過PIL.ExifTags　TAGS, GSPTAGS二個類別class，簡單地重溫了一下python資料結構形態dicitonary,以及dictionary內鍵功能（如本例中的items()）的進一步認識

最後，作了半天的元數據metadata抽取，到底有什麼意思呢？在表象上我們可看到的資料數據底下，還有這些由機器數位過程所產生記錄下來有關資料的資料。它能夠揭發的資訊，恐怕是原資料當事人也不知道的「自己」。如果你對元數據還是一無所知，不妨看看Pirivacy International 所製作的這支三分鐘小動畫。
https://privacyinternational.org/node/573　

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