There are 3 options to upload the image in the text box.

* Drag and drop.

* Copy and paste.

* Click on the  "image button" on the toolbar in the comment box.

 Click on the upload option.

Click on the "Send it to Server option" and then click "OK"  to upload or "Cancel" to go back.

Note: If you see Image source URL is missing then click on send it to the server button.