1) Sometimes it's not useful to search only by name or by ISBN on internet sites. I think it's better to do a search-area or something like this, where you can enter all the information you know about this book (for example, you know author and year). And then search this book. Because there are a lot of internet sites, which can be added as plugins, but which returns to much results when searching only by title or by name.
2) Author field in bookcard should has separate fields for Name, Lastname. I think, you should do a "Add author" button in bookcard, so you can add as many authors to each book, as you wish.
3) When scanning a book cover and clicking "cancel", the program crashes.
Sorry for my English.