diff --git a/src/c3nav/mapdata/api.py b/src/c3nav/mapdata/api.py
index 85853229..cf7bfb98 100644
--- a/src/c3nav/mapdata/api.py
+++ b/src/c3nav/mapdata/api.py
@@ -1,7 +1,10 @@
 import mimetypes
+import os
 from collections import namedtuple
+from datetime import datetime
 from functools import wraps
 
+import pytz
 from django.core.cache import cache
 from django.db.models import Prefetch
 from django.http import HttpResponse
@@ -378,7 +381,11 @@ class SourceViewSet(MapdataViewSet):
 
     def _image(self, request, pk=None):
         source = self.get_object()
-        return HttpResponse(open(source.filepath, 'rb'), content_type=mimetypes.guess_type(source.name)[0])
+        last_modified = datetime.utcfromtimestamp(os.path.getmtime(source.filepath)).replace(tzinfo=pytz.utc)
+        response = get_conditional_response(request, last_modified=last_modified)
+        if response is None:
+            response = HttpResponse(open(source.filepath, 'rb'), content_type=mimetypes.guess_type(source.name)[0])
+        return response
 
 
 class AccessRestrictionViewSet(MapdataViewSet):