From the Wikipedia entry on the origins of the scrapbook in the 15th century and their ongoing function as self-portraits:
From the standpoint of the psychology of authorship, it is noteworthy that keeping notebooks is in itself a kind of tradition among litterateurs. A commonplace book of literary memoranda may serve as a symbol to the keeper, therefore, of the person’s literary identity (or something psychologically not far-removed), quite apart from its obvious value as a written record. That commonplace books (and other personal note-books) can enjoy this special status is supported by the fact that authors frequently treat their notebooks as quasi-works, giving them elaborate titles, compiling them neatly from rough notes, recompiling still neater revisions of them later, and preserving them with a special devotion and care that seems out of proportion to their apparent function as working materials.
The writing being performed via collecting is thus somewhat unconscious; the sum greater than its parts.
In our age, visual communication is as commonplace as literacy. Thus, for at least the last century, scrapbooks have consisted of both clever phrases and the equally smart typography in which they are set, of notions of selfhood as well as the fashion with which these identities are performed.
Tumblr circa 1912
Recent tools like Ffffound, Tumblr, Polyvore and Pinterest not only facilitate the practice of collecting but, also, transform this once personal process into both a performance and/or a collaborative process.