This error message occurs when you’re using an Applet that has an Image URL ingredient, but the content posted does not contain an image.
If you are seeing this error message often, consider using an Applet without the Image URL ingredient.
Here is an example to help explain further. This Applet below will publish all of your Tumblr posts to Twitter, and it has an Image URL ingredient. If you publish a Tumblr post with an image, the image will post to Twitter successfully. However, if your Tumblr post does not have an image, the "image not found" message will appear on Twitter.