diff --git a/Dockerfile.backend b/Dockerfile.backend
index 8968392..10e7423 100644
--- a/Dockerfile.backend
+++ b/Dockerfile.backend
@@ -2,9 +2,10 @@ FROM python:3.11-slim
 
 WORKDIR /app
 
-# Install system dependencies
+# Install system dependencies (tkinter needed by app/core processing)
 RUN apt-get update && apt-get install -y --no-install-recommends \
     gcc \
+    python3-tk \
     && rm -rf /var/lib/apt/lists/*
 
 # Install Python dependencies