you can try to use "insertInlinePictureFromBase64".
Example:
var img = ''
Word.run(function (context) {
var body = context.document.body;
body.insertInlinePictureFromBase64(img, 'End');
return context.sync().then(function () {
app.showNotification('Image inserted successfully.');
});
})
.catch(function (error) {
app.showNotification("Error: " + JSON.stringify(error));
if (error instanceof OfficeExtension.Error) {
app.showNotification("Debug info: " + JSON.stringify(error.debugInfo));
}
});
Reference:
Inserting a base64 encoded image into a Word 2016 document
Other references:
InlinePicture object (JavaScript API for Word)
Body object (JavaScript API for Word)