Originally Posted by Maggie-Me
I do it one of two ways... easy way, I re-convert the ePub, make sure you have have insert metadata checked off under structure detection in Calibre.
Doesn't seem to change anything else in the ePub just adds the cover and the metadata
The other way is to download the jpeg from google or some where and insert it using Sigil
You can just paste the jpeg into the appropriate place in Calibre's 'Edit Metadata' window without going through Sigil. That worked for me on the NC before it got wrapped & put under the tree. Well mostly except for the cover problems that other's have previously mentioned that are usually corrected by doing a conversion from epub to epub.