diff --git a/.env.example b/.env.example
index b830272..ef12219 100644
--- a/.env.example
+++ b/.env.example
@@ -92,6 +92,14 @@ THUMB_WIDTH=160
 THUMB_HEIGHT=160
 PREVIEW_WIDTH=1920
 PREVIEW_HEIGHT=1080
+# Largest source image (in pixels, width×height) decoded to build a thumbnail or
+# preview; bigger images get a placeholder. Bounds a decompression bomb and the
+# per-image RAM cost. Default ~300 Mpx (e.g. 13000×17000).
+THUMB_MAX_PIXELS=300000000
+# How many thumbnails/previews may be generated at once. Each resize already uses
+# every core, so a burst of large images otherwise pegs the CPU and RAM. 0 = auto
+# (half the available CPUs).
+THUMB_CONCURRENCY=0
 
 # ---------------------------------------------------------------------------
 # Import