Well there is no way to directly edit the source graphics and use them in a stripcreator comic strip. If you are talking about taking the pictures and using them in your own online strip away from SC.com, then that's a different story.
Some of the graphics are public domain, but others belong to artists who allowed SC.com the rights to use them for SC, but did not give the rights to edit them for our own non-SC strips, or to use them elsewhere.
So I guess the short answer is "no" in all cases.