I exerienced the same problem discussed in a previous post.
I am running Joomla 2.5.7 and Book Library 2.2 and use the Allarounder-j1.6 template (I tested also the default template).
My covers are showing up in the List, in the individual Book Listing but not in the Gallery View. All images conform to your limits.
I made this modification (as previously suggested) but the problem is'nt resolved.
if($imageURL != '' && substr($imageURL,0,4) != "http"
$imageURL = 'pacinottiacademy.altervista.org'.
if($imageURL != ''
echo '<img src="'.$imageURL.'" alt="cover" border="0" height="50" ' ;
All other functions of the component are working very fine !!!