If you want an image to appear when viewing the document, you have to access: Settings > Basic Settings > References . Click on the Reference of the document type where you want to add the image.
In the attachments section of the toolbar click on the icon showing the image, in the URL field you can enter the URL of your image.
To have it correctly reflected in the document template, you must access: Settings > My Company > My Templates. Click onthe desired template, enter the Remarks and Attachments taband check the Attachments as image option.
Similarly if you have created a table in the Attachments field of the Reference, you must check the Attachments as image boxin the Document Template, so you can display it in the template.
The image to use must be a public image, that is to say that it has a URL, if your image is not public there are endless applications and free web pages that allow you to create a URL for your image.