<img src="https://cdn-images-1.medium.com/max/735/1*KEiF2KBM-bYfZ2gKLcDEeQ@2x.png"; />
It's better to use url link of the images in the HTML tag instead of any base64 image code as the API currently doesn't have the feature to convert it back to image.
Maybe in future they introduce this dealing with base64 format.
Also the url link should be public and accessible to ringcentral to get the image from the location
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