For embedded graphics, legends, and insets, I like to use the BORDER=TRUE option on the LAYOUT GRIDDED statement to put a box around the inner picture. If you add a border, you might also want to use the PAD=5 option to add a little padding to the plot area. Lastly, I like to use the OPAQUE=TRUE option so that the inside image obscurs any grid lines or reference lines in the main graph.