Originally Posted by meme
You just need to right-click on the cover image and select Add Semantics -> Cover Image (along with adding the semantic type to the HTML file including the image). Sigil no longer tries to guess which image is your cover to avoid a few issues some people had:
- Implement issue 1414: Cover semantic should not be added automatically.
Add Semantics only determines what goes into the <guide> section of content.opf and works fine. The missing line is in the meta data.