For example - take this cat in a Santa hat. I have no idea where this image came from. I mean, not originally. All I know is, I did a Google Image search for "cat in a Santa hat," and this came up. Perhaps services like Google Image are partly to blame in this credit conundrum? I mean, I saved the picture from this site, but who actually took the photo? I have no idea. Because eglobe1 didn't tell me - and I'm sure they don't know, either. I think it's important to remember in all this ethics brew-ha-ha that images have often been recycled so many times, we don't always know where they originated. Part of the onus is on the creator of the work to make it explicitly clear that they must be credited in all usage (as I'm sure was the case in the Richter Scales incident referenced in Derek's post.)
YouTube and other video sites have solved this problem by using a system of embeds - Flickr operates the same way. (Of course where the content comes from before it's on YouTube or Flickr may still be in question, but once it's on those sites, clicks are automatically linked back to them.) Perhaps "right-clicking" should be disabled by default on all online images as a way of preventing use without credit? That way, for the average blogger, any pictures that are embeddable are also legal to use.
a hole in the head
Originally uploaded by changoblanco