An interesting discussion about the two from Philip Nel… he begins:
“If in comics the gutters between panels enlist the reader’s imagination to create closure, in picture books it is the turning of the page that prompts the act of closure. If comics rely on juxtapositions between “pictorial and other images in deliberate sequence” (to quote Scott McCloud ), picture books more commonly rely on juxtapositions between text and image. If comics ordinarily depict movement in time within a single page, in picture books time tends to unfold over many pages.
These three “generic differences” apply broadly to comics and picture books, yet so many exceptions permeate the two genres that any boundary between them has to be highly porous. Picture books and comics are kin: adjacent branches of the same literary-artistic family tree, cousins with slightly different expectations of their readers. They are not fundamentally different genres. To put this in terms of the biological taxonomy we learned back in grade school (kingdom, phylum, class, order, family, genus, species), the distinctions between the two rank down at the end of smallest differentiation—the “species” end. Comics and picture books differ in degree, rather than in kind. As this essay will show, the accepted “truths” about differences between picture books and comics mark little more than different emphases, or tendencies, not absolute divisions. The kinship between them calls into question the fitness of the term “genre.” At the least, it requires that we consciously reflect on what we mean by this term—the full significance of which may go beyond form to embrace context, readership, and even material modes of production.” (p.445)
Ref: Philip Nel ‘Same Genus, Different Species?: Comics and Picture Books’ Children’s Literature Association Quarterly 37.4 (Winter 2012): 445-453.