Documentation / Content
SwiftLing translates two things about images.
Alt texts and captions
Alt texts and captions appear in the editor with the other texts of the page: Alt text, Caption. Alt texts of media library files are translated too.
Another image for a language
For an image that carries text, or should differ in a country, use an image field: in the editor press Choose the image for this language, pick an image from the media library, and Use this image. The translated page shows it in that language only.
Videos and audio are listed as Video or audio fields in the same way.