Picture frame

Q: How do I put the frame around my pictures that I am posting..like an outline around the photos?
A: design>template designer>advanced>images>background colour/border colour

Choose your colours

Press [apply to blog] to save changes.

source: http://www.google.com/support/forum/p/blogger/thread?fid=341a24d7a830e50d00049f6b47b8c407&hl=en