[GeoffR]

I noticed that the books I downloaded from Kobo had cover images of various aspect ratios, but were displayed nicely with a properly fitting box around the image, whereas the covers of sideloaded books (whether sent from Calibre or copied manually) were either distorted to fit a 4:3 aspect ratio or did not fit the 4:3 box around the image, leaving ugly while space.

Sending the covers seperately from the book using Calibre also distorts the cover into a 4:3 aspect ratio too.

But if I copy the cover manually from the Calibre library onto my Glo, overwriting the existing cover image ending in N3_FULL.parsed, then the cover is nicely displayed without distortion and with a properly fitting box, just as with the books downloaded from Kobo.

The pictures of the three books on the left show the difference, the first photo is with the books sent from Calibre (same result as sending covers from calibre), the second with the covers copied manually. (The two books on the right of the home screen are kepubs downloaded directly from Kobo).