Fix overlay scaling mismatch by applying DPI scale factor to bounding boxes

app.py

@@ -261,15 +261,20 @@ def render_page_with_overlay(
 
     ordered = order_blocks(blocks, order_mode)
 
+    scale = dpi / 72.0
+
     # Try to use a default font; if not available, PIL will still draw text.
     try:
         font = ImageFont.load_default()
     except Exception:
         font = None
 
+    def _scale_rect(rect):
+        x0, y0, x1, y1 = rect
+        return (int(x0 * scale), int(y0 * scale), int(x1 * scale), int(y1 * scale))
+
     for rank, (idx, b) in enumerate(ordered, start=1):
-        x0, y0, x1, y1 = b.bbox
-        r = _rect_i((x0, y0, x1, y1))
+        r = _scale_rect(b.bbox)
 
         is_text = (b.block_type == 0 and b.text.strip() != "")
         is_math = is_text and _looks_like_math(b.text)
@@ -285,8 +290,7 @@ def render_page_with_overlay(
 
         if show_spans and b.block_type == 0:
             for sp in b.spans:
-                sx0, sy0, sx1, sy1 = sp.bbox
-                sr = _rect_i((sx0, sy0, sx1, sy1))
+                sr = _scale_rect(sp.bbox)
                 draw.rectangle(sr, outline=colors['span_border'], width=1)
 
     return img