The 'See Images in Gallery' setting controls if images are visible to the Gallery Viewer
You can choose if the images used for Book covers are visible to the phones gallery viewer
The gallery viewer should pick the changes up automatically, but you may need to restart it on some phones
Hiding the images from the viewer may speed up some viewers if you have a lot of images for the app
Use the 'Sync With Gallery' setting to re-sync the images with the gallery manually
Images can be accessed from
Pressing this setting, toggles if the gallery can see the app images
the Gallery app may need restarting to pick up the changes
Various apps offer the ability to edit image files
most will provide functions such as rotate, auto-contrast and crop
You can start an image editing app directly from the Image Menu on the Edit Details Screen
note that the Gallery Viewer will save new images with a -1 or -2 etc suffix when accessed directly;
in these cases delete the un-suffixed file and rename the suffixed file to have no suffixes
eg. an original file '789.jpg', when edited via Gallery Viewer, creates a file '789-1.jpg'
delete the original '789.jpg' file and then rename '789-1.jpg' to '789.jpg'
the Book Library App will use the '789.jpg' file next time it displays the image