Update.

app/Book.php

@@ -18,7 +18,7 @@ class Book extends Entity
         return baseUrl('/books/' . urlencode($this->slug));
     }
 
-    public function getBookCover($size = 120)
+    public function getBookCover()
     {
         $default = baseUrl('/default.png');
         $image = $this->image;

resources/views/books/grid-item.blade.php

@@ -7,7 +7,7 @@
     </h4>
     <div class="gallery-image">
         <a class="text-book entity-list-item-link" href="{{$book->getUrl()}}">
-        <img src="{{$book->getBookCover(192)}}" alt="{{$book->name}}">
+        <img src="{{$book->getBookCover()}}" alt="{{$book->name}}">
         </a>
     </div>
     @if(isset($book->searchSnippet))