It used to be that collectors of books would paste an 'ex libris' label in each of their lovely acquisitions. Basically it was a little certificate of ownership that indicated, "this is my treasure, hands-off unless I deem you worthy of loaning this book, and even then you better damn well return it", or sentiments of that nature.
It used to be that persons with money would have their book plates designed by an artist of renown, making them quite collectible in and of themselves.
Then, back in the '60s, there were adolescents like me who bought, for a couple of bucks, a little box of mass-produced bookplates for my mass-produced books. Tolkien's Middle Earth had a huge upswelling back then and I had assumed this was an image of Bilbo Baggins, even though this guy doesn't have big furry feet.
I think I saw this same bookplate design at B Daltons a couple of years ago. Every once in a while as I look through books that have been with me for years, I see one of these with my name signed on it and think again, "this is my treasure . . . "