That particular image was actually edited in a photoediting program like Photoshop; the space and line are part of the image itself.
There are a couple of ways to get this look. First, you could create an "action" or "macro" in your image editor that adds whitespace and a thin border (in Photoshop, for ex., you'd use the "canvas size" dialogue twice, one to add a white border then another for the colored line).
My suggestion, however, would be to do this through CSS. Add something like
CODE
.blogbody .img { padding: 8px; border: 1px solid #666; }
to your stylesheet; then you could easily change the color of all the lines if you change your site's layout or color scheme.