diff --git a/boards/forms.py b/boards/forms.py
--- a/boards/forms.py
+++ b/boards/forms.py
@@ -1,8 +1,9 @@
 import hashlib
 import re
 import time
+import logging
+import pytz
 
-import pytz
 from django import forms
 from django.core.files.uploadedfile import SimpleUploadedFile
 from django.core.exceptions import ObjectDoesNotExist
@@ -45,6 +46,16 @@ TEXTAREA_ROWS = 4
 
 TRIPCODE_DELIM = '#'
 
+# TODO Maybe this may be converted into the database table?
+MIMETYPE_EXTENSIONS = {
+    'image/jpeg': 'jpeg',
+    'image/png': 'png',
+    'image/gif': 'gif',
+    'video/webm': 'webm',
+    'application/pdf': 'pdf',
+    'x-diff': 'diff',
+}
+
 
 def get_timezones():
     timezones = []
@@ -160,11 +171,17 @@ class PostForm(NeboardForm):
 
     def _update_file_extension(self, file):
         if file:
-            extension = get_file_mimetype(file)
-            filename = file.name.split(FILE_EXTENSION_DELIMITER, 1)[0]
-            new_filename = filename + FILE_EXTENSION_DELIMITER + extension
+            mimetype = get_file_mimetype(file)
+            extension = MIMETYPE_EXTENSIONS.get(mimetype)
+            if extension:
+                filename = file.name.split(FILE_EXTENSION_DELIMITER, 1)[0]
+                new_filename = filename + FILE_EXTENSION_DELIMITER + extension
 
-            file.name = new_filename
+                file.name = new_filename
+            else:
+                logger = logging.getLogger('boards.forms.extension')
+
+                logger.info('Unrecognized file mimetype: {}'.format(mimetype))
 
     def clean_title(self):
         title = self.cleaned_data['title']
diff --git a/boards/models/attachment/__init__.py b/boards/models/attachment/__init__.py
--- a/boards/models/attachment/__init__.py
+++ b/boards/models/attachment/__init__.py
@@ -12,7 +12,8 @@ class AttachmentManager(models.Manager):
         if len(existing) > 0:
             attachment = existing[0]
         else:
-            file_type = get_file_mimetype(file)
+            # FIXME Use full mimetype here, need to modify viewers too
+            file_type = get_file_mimetype(file).split('/')[-1]
             attachment = self.create(file=file, mimetype=file_type,
                                      hash=file_hash)
 
diff --git a/boards/static/js/image.js b/boards/static/js/image.js
--- a/boards/static/js/image.js
+++ b/boards/static/js/image.js
@@ -112,13 +112,13 @@ PopupImageViewer.prototype.view = functi
             .attr('id', thumb_id)
             .attr('src', postNode.attr('href'))
             .attr(ATTR_SCALE, scale)
-            .appendTo(postNode)
             .css({
                 'width': img_w,
                 'height': img_h,
                 'left': (win_w - img_w) / 2,
                 'top': ((win_h - img_h) / 2)
             })
+            .appendTo(postNode)
         //scaling preview
         .mousewheel(function(event, delta) {
             var cx = event.originalEvent.clientX;
diff --git a/boards/utils.py b/boards/utils.py
--- a/boards/utils.py
+++ b/boards/utils.py
@@ -129,10 +129,7 @@ def validate_file_size(size: int):
 
 def get_upload_filename(model_instance, old_filename):
     # TODO Use something other than random number in file name
-    if hasattr(model_instance, 'mimetype'):
-        extension = model_instance.mimetype
-    else:
-        extension = old_filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
+    extension = old_filename.split(FILE_EXTENSION_DELIMITER)[-1:][0]
     new_name = '{}{}.{}'.format(
         str(int(time.mktime(time.gmtime()))),
         str(int(random() * 1000)),
@@ -144,5 +141,4 @@ def get_upload_filename(model_instance, 
 
 
 def get_file_mimetype(file) -> str:
-    return magic.from_buffer(file.chunks().__next__(), mime=True) \
-        .decode().split('/')[-1]
+    return magic.from_buffer(file.chunks().__next__(), mime=True).decode()