I have to say that the 1% of people that are out to steal your images are most definately smart enough to print-screen or use another browser to steal the images (they do it for a living), while the "locking" code just hurts mainstream members.
If the true motive behind locking the images is to keep membership recurring just say so, if not, it just won't work.
Personally, I keep coming back for the consistently good new material each month.
thx,
-Chell