helleborine - 2:30 pm on Feb 28, 2013 (gmt 0)
My personal, non-legal opinion is that the fact that the only options available are (1) robots.txt to get out of Google Images or (2) complex redirects that may or may not penalized is quite unfair.
Had Google (and Bing, let's not forget Bing is just as bad) provided us with means to only allow thumbnail display, it would be different.
I'd still be unhappy that the default state is "we grab our images" unless we code a line on our pages that says "no you don't."
I'm not sure how that would fly in court because the option of blocking Google Images bot with robots.txt does exist.