Hiding the Second Life Interface:
To make the whole User Interface (UI) disappear, you can either use a shortcut or through the advanced menu.
Press Ctrl-Alt-⇧ Shift-D to make the Advanced menu appear.
Then go to 'Rendering', unclick 'Show UI'. That will make all the UI disappear. If you want to get the UI back use the shortcut: Ctrl-Alt-F1.
Stopping your shot with Snapz Pro X: