diff --git a/src/snek/system/template.py b/src/snek/system/template.py
index 6460ff1..fa8a749 100644
--- a/src/snek/system/template.py
+++ b/src/snek/system/template.py
@@ -181,12 +181,12 @@ def enrich_image_rendering(text):
     soup = BeautifulSoup(text, "html.parser")
     for element in soup.find_all("img"):
         if element.attrs["src"].startswith("/"):
-            element.attrs["src"] += "?width=240&height=240&format=webp"
+            element.attrs["src"] += "?width=240&height=240"
             picture_template = f'''
                                 <picture>
                                     <source srcset="{element.attrs["src"]}" type="{mimetypes.guess_type(element.attrs["src"])[0]}" />
-                                    <source srcset="{element.attrs["src"]}" type="image/webp" />
-                                    <img src="{element.attrs["src"]}" title="{element.attrs["src"]}" alt="{element.attrs["src"]}" />
+                                    <source srcset="{element.attrs["src"]}&format=webp" type="image/webp" />
+                                    <img src="{element.attrs["src"]}&format=png" title="{element.attrs["src"]}" alt="{element.attrs["src"]}" />
                                 </picture>'''
             element.replace_with(BeautifulSoup(picture_template, "html.parser"))
     return str(soup)
diff --git a/src/snek/view/channel.py b/src/snek/view/channel.py
index 84ee2cd..90d7c59 100644
--- a/src/snek/view/channel.py
+++ b/src/snek/view/channel.py
@@ -1,5 +1,6 @@
 import asyncio
 import mimetypes
+from os.path import isfile
 
 from PIL import Image
 import pillow_heif.HeifImagePlugin
@@ -17,7 +18,7 @@ class ChannelAttachmentView(BaseView):
             relative_url=relative_path
         )
 
-        if not channel_attachment:
+        if not channel_attachment or not isfile(channel_attachment["path"]):
             return web.HTTPNotFound()
 
         original_format = mimetypes.guess_type(channel_attachment["path"])[0]