The function parse-exif-data returns a structure containing all the meta information about the image file:

  cl-user(10): (describe
		(parse-exif-data
                 "c:/pictures/_TMP/20041128-1515-1200-S1IS.JPG"))
  #<exif-info @ #x2072d512> is a structure of type exif-info.
  It has these slots:
   file               "c:/pictures/_TMP/20041128-1515-1200-S1IS.JPG"
   make               "Canon"
   model              "Canon PowerShot S1 IS"
   date               "2004:11:28 15:15:12"
   comment            ""
   exposure           0.00125
   f-number           4.5
   iso-rating         nil
   exposure-bias-value  0.0
   subject-distance   nil
   flash              t
   focal-length       48.578
   image-width        2048
   image-length       1536
  cl-user(11):