There is a REST API call to Retrieves a user's avatar or profile image. The retrieved image is a base64 encoded string packaged in a JSON structure. Use /avatar/{userNameOrID} to retrieve any user's avatar or use /avatar/current for the avatar of current logged in user.
GET /rest/bpm/wle/v1/avatar/{userNameOrID}
Then in custom html you can embed the image data using following syntax
<img src="data:image/png;base64,iVBORw0KGgoAAAANS..." />
This is based on possibility we will post a working example to test how it actually works.