Rotate thumbnails according to exif orientation

boop.py

 from operator import itemgetter
 
 from jinja2 import Environment, PackageLoader, select_autoescape
-from PIL import Image
+from PIL import Image, ExifTags
 
 from configuration import SITE_TITLE, THEME
 
 
 
 def generate_thumb_file(output_path, photo):
+    orientation_key = get_orientation_exif_key()
+    size = (440, 264)
+
     with Image.open(photo["path"]) as image:
-        size = (440, 264)
+        # First, make sure image is correctly oriented
+        exif = image._getexif()
+        if exif[orientation_key] == 3:
+            image = image.rotate(180, expand=True)
+        elif exif[orientation_key] == 6:
+            image = image.rotate(270, expand=True)
+        elif exif[orientation_key] == 8:
+            image = image.rotate(90, expand=True)
+
         w, h = image.size
         if w > size[0] and h > size[1]:
             # If the original file is larger in width AND height, we resize
         image.save(output_path)
 
 
+def get_orientation_exif_key():
+    for (key, tag) in ExifTags.TAGS.items():
+        if tag == "Orientation":
+            return key
+
+
 def main():
     pictures_folder = os.path.join(os.curdir, PICTURES_DIR_NAME)
     galleries = list(list_galleries_in(pictures_folder))