diff --git a/web/work_plane.js b/web/work_plane.js
index 00f33f4..a224ccc 100644
--- a/web/work_plane.js
+++ b/web/work_plane.js
@@ -61,12 +61,17 @@ function startRgbLoop() {
   }
 
   function syncOverlaySize() {
-    overlay.width = img.naturalWidth || 640;
-    overlay.height = img.naturalHeight || 480;
+    // Setting width/height on a canvas wipes its content. Only re-set when
+    // the image resolution actually changes (rare) so the ROI overlay survives
+    // each RGB live-refresh tick.
+    const w = img.naturalWidth || 640;
+    const h = img.naturalHeight || 480;
+    if (overlay.width !== w) overlay.width = w;
+    if (overlay.height !== h) overlay.height = h;
     overlay.style.width = img.clientWidth + 'px';
     overlay.style.height = img.clientHeight + 'px';
   }
-  img.addEventListener('load', syncOverlaySize);
+  img.addEventListener('load', () => { syncOverlaySize(); drawOverlay(); });
 
   // Two-click ROI: 1st click = corner A, 2nd click = corner B (rectangle
   // defined). 3rd click starts a new selection.