diff --git a/app/scodoc/sco_photos.py b/app/scodoc/sco_photos.py
index c0f3cbd8..37908d51 100644
--- a/app/scodoc/sco_photos.py
+++ b/app/scodoc/sco_photos.py
@@ -73,7 +73,7 @@ from config import Config
 PHOTO_DIR = os.path.join(Config.SCODOC_VAR_DIR, "photos")
 ICONS_DIR = os.path.join(Config.SCODOC_DIR, "app", "static", "icons")
 UNKNOWN_IMAGE_PATH = os.path.join(ICONS_DIR, "unknown.jpg")
-UNKNOWN_IMAGE_URL = "get_photo_image?etudid="  # with empty etudid => unknown face image
+
 IMAGE_EXT = ".jpg"
 JPG_QUALITY = 0.92
 REDUCED_HEIGHT = 90  # pixels
@@ -81,6 +81,11 @@ MAX_FILE_SIZE = 4 * 1024 * 1024  # max allowed size for uploaded image, in bytes
 H90 = ".h90"  # suffix for reduced size images
 
 
+def unknown_image_url() -> str:
+    "URL for 'unkwown' face image"
+    return url_for("scolar.get_photo_image", scodoc_dept=g.scodoc_dept, etudid="")
+
+
 def photo_portal_url(etud):
     """Returns external URL to retreive photo on portal,
     or None if no portal configured"""
@@ -118,7 +123,7 @@ def etud_photo_url(etud: dict, size="small", fast=False) -> str:
         ext_url = photo_portal_url(etud)
         if not ext_url:
             # fallback: Photo "unknown"
-            photo_url = scu.ScoURL() + "/" + UNKNOWN_IMAGE_URL
+            photo_url = unknown_image_url()
         else:
             # essaie de copier la photo du portail
             new_path, _ = copy_portal_photo_to_fs(etud)
@@ -128,7 +133,7 @@ def etud_photo_url(etud: dict, size="small", fast=False) -> str:
                 if scu.CONFIG.PUBLISH_PORTAL_PHOTO_URL:
                     photo_url = ext_url
                 else:
-                    photo_url = scu.ScoURL() + "/" + UNKNOWN_IMAGE_URL
+                    photo_url = unknown_image_url()
     return photo_url
 
 
@@ -143,7 +148,8 @@ def get_photo_image(etudid=None, size="small"):
         filename = photo_pathname(etud.photo_filename, size=size)
         if not filename:
             filename = UNKNOWN_IMAGE_PATH
-    return _http_jpeg_file(filename)
+    r = _http_jpeg_file(filename)
+    return r
 
 
 def _http_jpeg_file(filename):
@@ -166,7 +172,7 @@ def _http_jpeg_file(filename):
         except ValueError:
             mod_since = None
         if (mod_since is not None) and last_modified <= mod_since:
-            return "", 304  # not modified
+            return make_response(b"", 304)  # not modified
     #
     last_modified_str = time.strftime(
         "%a, %d %b %Y %H:%M:%S GMT", time.gmtime(last_modified)
@@ -183,7 +189,7 @@ def etud_photo_is_local(etud: dict, size="small"):
     return photo_pathname(etud["photo_filename"], size=size)
 
 
-def etud_photo_html(etud: dict = None, etudid=None, title=None, size="small"):
+def etud_photo_html(etud: dict = None, etudid=None, title=None, size="small") -> str:
     """HTML img tag for the photo, either in small size (h90)
     or original size (size=="orig")
     """
@@ -201,7 +207,7 @@ def etud_photo_html(etud: dict = None, etudid=None, title=None, size="small"):
         title = nom
     if not etud_photo_is_local(etud):
         fallback = (
-            """onerror='this.onerror = null; this.src="%s"'""" % UNKNOWN_IMAGE_URL
+            f"""onerror='this.onerror = null; this.src="{unknown_image_url()}"'"""
         )
     else:
         fallback = ""
@@ -218,7 +224,7 @@ def etud_photo_html(etud: dict = None, etudid=None, title=None, size="small"):
     )
 
 
-def etud_photo_orig_html(etud=None, etudid=None, title=None):
+def etud_photo_orig_html(etud=None, etudid=None, title=None) -> str:
     """HTML img tag for the photo, in full size.
     Full-size images are always stored locally in the filesystem.
     They are the original uploaded images, converted in jpeg.