lucy24 - 11:29 pm on Feb 3, 2013 (gmt 0)

Hasn't that been entirely replaced by snapshots?

Snapshot, thumbnail, whatever you call it so long as it's cached.

if you allow them to index then whatever else they do with the image, including hotlinking, is kind of fair game as long as it's used to promote your image.

Now, wait. What does "promote your image" mean? From the webmaster's POV, image search means: Find sites that include pictures of X. And then the searcher goes to your site.

Only in the rarest case would you want it to mean simply: Find pictures of X in isolation. ("I found a photo of {famous person} doing {silly or illegal act} and I want the entire world to see it by any means possible.")

The still-unanswered question is: What proportion of image searchers fall into this second group? They don't intend to go to any site, they just want to look at pictures. Those are the ones you can safely block-- but only if you can do it without also blocking the first group.