What is the ruling on a wife adorning herself for her husband with voice and image via the Internet, while the husband is not certain that there are no intruders on the connection?

There is no harm in the wife being seen in that state if one is secure from others seeing her. However, it is advisable to refrain from this to be cautious against others entering, and so that desire is not aroused at a time when it cannot be fulfilled in a permissible manner, which might lead to looking towards the unlawful.