Why the black border? Hmm. While I like the expanse of white sky, I didn't want the white-ness to overwhelm. The black border only works because there is heavy black within the picture too; otherwise it would be overwhelming. Also, I thought the contrast between the clean, graphic, black frame and the messiness of the family candids balanced each other out. And, it draws attention to the white negative space created by the black shapes.
Why such a thick border? It makes me think of postcards, or posters (strange that I think of both, since the scale is so different). Actually, none of this reasoning happened when I added the border. I just thought it looked interesting, and came up with reasons for this blog post.