diff --git a/nanobot/agent/loop.py b/nanobot/agent/loop.py
index 4adc798..b402ea0 100644
--- a/nanobot/agent/loop.py
+++ b/nanobot/agent/loop.py
@@ -469,6 +469,14 @@ class AgentLoop:
                 content = entry["content"]
                 if len(content) > self._TOOL_RESULT_MAX_CHARS:
                     entry["content"] = content[:self._TOOL_RESULT_MAX_CHARS] + "\n... (truncated)"
+            if entry.get("role") == "user" and isinstance(entry.get("content"), list):
+                entry["content"] = [
+                    {"type": "text", "text": "[image]"} if (
+                        c.get("type") == "image_url"
+                        and c.get("image_url", {}).get("url", "").startswith("data:image/")
+                    ) else c
+                    for c in entry["content"]
+                ]
             entry.setdefault("timestamp", datetime.now().isoformat())
             session.messages.append(entry)
         session.updated_at = datetime.now()
diff --git a/nanobot/utils/helpers.py b/nanobot/utils/helpers.py
index 62f80ac..06d8fd5 100644
--- a/nanobot/utils/helpers.py
+++ b/nanobot/utils/helpers.py
@@ -3,7 +3,6 @@
 from pathlib import Path
 from datetime import datetime
 
-
 def ensure_dir(path: Path) -> Path:
     """Ensure a directory exists, creating it if necessary."""
     path.mkdir(parents=True, exist_ok=True)
@@ -77,4 +76,4 @@ def parse_session_key(key: str) -> tuple[str, str]:
     parts = key.split(":", 1)
     if len(parts) != 2:
         raise ValueError(f"Invalid session key: {key}")
-    return parts[0], parts[1]
+    return parts[0], parts[1]
\ No newline at end of file