diff --git a/mel/cmd/rotomapedit.py b/mel/cmd/rotomapedit.py
index 9875418f..ba96c483 100644
--- a/mel/cmd/rotomapedit.py
+++ b/mel/cmd/rotomapedit.py
@@ -16,6 +16,7 @@
     Press '2' for mask edit mode.
     Press '3' for bounding area mode.
     Press '4' for mole marking mode.
+    Press '5' for mole compare boundary mode.
     Press '0' for auto-mole debug mode.
 
 In 'mole edit' mode:
@@ -409,6 +410,41 @@ def on_key(self, editor, key):
             editor.show_current()
 
 
+class MoleCompareBoundaryController:
+    def __init__(self):
+        pass
+
+    def on_mouse_event(self, editor, event):
+        # Import pygame as late as possible, to avoid displaying its
+        # startup-text where it is not actually used.
+        import pygame
+
+        if event.type != pygame.MOUSEBUTTONDOWN:
+            return
+
+        key_mods = pygame.key.get_mods()
+        mouse_x, mouse_y = pygame.mouse.get_pos()
+
+        if event.button == 1:
+            if key_mods & pygame.KMOD_SHIFT:
+                editor.remove_mole(mouse_x, mouse_y)
+            else:
+                editor.add_mole(mouse_x, mouse_y)
+
+    def pre_key(self, editor, key):
+        pass
+
+    def on_key(self, editor, key):
+        # Import pygame as late as possible, to avoid displaying its
+        # startup-text where it is not actually used.
+        import pygame
+
+        if key == pygame.K_a:
+            is_alt = editor.marked_mole_overlay.is_accentuate_marked_mode
+            editor.marked_mole_overlay.is_accentuate_marked_mode = not is_alt
+            editor.show_current()
+
+
 class BoundingAreaController:
     def __init__(self):
         pass
@@ -468,6 +504,7 @@ def __init__(self, editor, follow, copy_to_clipboard, visit_list, logger):
         )
         self.maskedit_controller = MaskEditController()
         self.molemark_controller = MoleMarkController()
+        self.molecompareboundary_controller = MoleCompareBoundaryController()
         self.boundingarea_controller = BoundingAreaController()
         self.automoledebug_controller = AutomoleDebugController()
         self.current_controller = self.moleedit_controller
@@ -546,6 +583,11 @@ def on_key(self, editor, key):
             self.current_controller = self.molemark_controller
             self._logger.reset(mode="molemark")
             editor.set_molemark_mode()
+        elif key == pygame.K_5:
+            # Switch to mole compare boundary mode
+            self.current_controller = self.molecompareboundary_controller
+            self._logger.reset(mode="molecompareboundary")
+            editor.set_molecompareboundary_mode()
         elif key == pygame.K_b:
             # Go back in the visit list
             if self._visit_list:
diff --git a/mel/rotomap/display.py b/mel/rotomap/display.py
index 64780a98..7d57106d 100644
--- a/mel/rotomap/display.py
+++ b/mel/rotomap/display.py
@@ -265,6 +265,36 @@ def _draw_markers(self, image, transform):
         return image
 
 
+class MoleCompareBoundaryOverlay:
+    """An overlay to show how much context a rotomap compare window will
+    show."""
+
+    def __init__(self):
+        self.moles = None
+
+    def __call__(self, image, transform):
+        return self._draw(image, transform)
+
+    def _draw(self, image, transform):
+        # Reveal the moles that have been marked, whilst still showing
+        # markers. This is good for verifying that markers are actually
+        # positioned on moles.
+
+        mask_radius = 50
+
+        image = image.copy() // 2
+        mask = numpy.zeros((*image.shape[:2], 1), numpy.uint8)
+
+        for mole in self.moles:
+            x, y = transform.imagexy_to_transformedxy(mole["x"], mole["y"])
+            cv2.circle(mask, (x, y), mask_radius, 255, -1)
+
+        masked_faded = cv2.bitwise_and(image, image, mask=mask)
+        image = cv2.add(masked_faded, image)
+
+        return image
+
+
 class BoundingAreaOverlay:
     """An overlay to show the bounding area, if any."""
 
@@ -312,6 +342,7 @@ class EditorMode(enum.Enum):
     edit_mask = 2
     bounding_area = 3
     mole_mark = 4
+    mole_compare_boundary = 5
     debug_automole = 0
 
 
@@ -328,6 +359,7 @@ def __init__(self, directory_list, screen):
         self._follow = None
         self._mole_overlay = MoleMarkerOverlay(self._uuid_to_tricolour)
         self.marked_mole_overlay = MarkedMoleOverlay()
+        self.mole_compare_boundary_overlay = MoleCompareBoundaryOverlay()
         self.bounding_area_overlay = BoundingAreaOverlay()
         self._status_overlay = StatusOverlay()
         self.show_current()
@@ -363,6 +395,10 @@ def set_molemark_mode(self):
         self._mode = EditorMode.mole_mark
         self.show_current()
 
+    def set_molecompareboundary_mode(self):
+        self._mode = EditorMode.mole_compare_boundary
+        self.show_current()
+
     def set_status(self, text):
         self._status_overlay.text = text
 
@@ -471,6 +507,11 @@ def show_current(self):
         elif self._mode is EditorMode.mole_mark:
             self.marked_mole_overlay.moles = self.moledata.moles
             self.display.show_current(image, self.marked_mole_overlay)
+        elif self._mode is EditorMode.mole_compare_boundary:
+            self.mole_compare_boundary_overlay.moles = self.moledata.moles
+            self.display.show_current(
+                image, self.mole_compare_boundary_overlay
+            )
         else:
             raise Exception("Unknown mode", self._mode)