It is recommended that when used on Wikimedia projects images are given alternative texts − see http://enwp.org/WP:ALT
When using the "Use this file>Embed>Wikitext" feature, MultimediaViewer provides a wikitext snippet such as
[[File:Common_Kingfisher_Alcedo_atthis.jpg|thumb|Common Kingfisher Alcedo atthis]]
A fr.wp user pointed out in their feedback that the snippet should have an alt= element, to encourage this accessibility best practice.
(Marking as Unconfirmed as the risk of users leaving an empty alt seems high, and it seems that an empty alt is bad).