diff --git a/discord_webhook/webhook.py b/discord_webhook/webhook.py
index 7b1ff06..f46facd 100644
--- a/discord_webhook/webhook.py
+++ b/discord_webhook/webhook.py
@@ -126,7 +126,7 @@ def set_footer(self, text: str, **kwargs) -> None:
     def set_image(self, url: str, **kwargs: Union[str, int]) -> None:
         """
         Set the image that will be displayed in the embed.
-        :param str url: source url of image (only supports http(s) and attachments)
+        :param str url: source url of image (only supports http(s) and attachments). Local files must be added as a file to your webhook first, then be referenced as attachment://<image file name>
         :keyword str proxy_url: a proxied url of the image
         :keyword int height: height of image
         :keyword int width: width of image