It could be an issue on the onImageUpload callback in the summernote initialization. Basically, this callback will listen for image uploads and in the example, we're calling a separate javascript function (sendFile). The sendFile function will make an AJAX post to your application at a different endpoint and will handle the uploading to S3. The success callback of this AJAX request should return a hash with the URL of the S3 image. The success callback will create the image element with the URL from the returned hash and that will be what gets inserted.