Made this code a little more robust.

dlib/image_keypoint/hashed_feature_image.h

@@ -247,6 +247,8 @@ namespace dlib
     {
         fe.load(img);
 
+        if (fe.size() != 0)
+        {
             feats.set_size(fe.nr(), fe.nc());
             for (long r = 0; r < feats.nr(); ++r)
             {
@@ -255,6 +257,12 @@ namespace dlib
                     feats[r][c] = phash(fe(r,c));
                 }
             }
+        }
+        else
+        {
+            feats.set_size(0,0);
+        }
+
         fe.unload();
     }