How do i get my pictures back?? please help?

Ok so every time i transfer my pictures from my camara (casio) to my computer the pictures on my camara get deleted! Like i want to make a copy to the computer without deleting them. Is there any way to get my pictures back on my camara because if my laptop crashes all my disney ( and more) photos will be gone! and how do avoid them from being deleted in the first place??