With 'editor.upload.image.base64' setting, you may determine if you will use base64 image when you upload images (default - false).
If set to true, when an image is inserted, the image will not be uploaded to the server but, instead, will be encoded into base64 image and displayed in the body.
synapeditor.config.js
{ 'editor.upload.image.base64': false, }
Example Result of Image Insertion
<div class="se-contents" style="font-family: Arial, Helvetica, sans-serif; font-size: 11pt; line-height: 1.2; padding: 25px;"> <p style="overflow-wrap: break-word; margin: 16px 0px; display: block;"> <span></span> <span class="se-drawing-object-wrapper se-image" style="vertical-align: baseline; text-indent: 0px; display: inline-block;"> <img src="data:image/png;base64,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" style="vertical-align: bottom; width: 78px; height: 84px;"> </span> <span></span> </p> </div>