But I also know that there are certain images which are often hotlinked from my (work) web site quite often ... and copied quite often too, I know how I trace them, I know what I can (and very occasionally DO do) if I find them elsewhere in this way, and (sorry) I don't have the time to risk finding myself in the firing line over a picture of an electrodiesel

Slightly off topic, but reminds me of a time another seller hotlinked to an image of something I was selling on ebay. They linked the image directly to my website. Got the link changed on my listing then changed the image that was shown in the old location to something slightly more inappropriate. Amusing to see their listing with this picture and they become NARU (Not a Registered User - probably due to showing an inappropriate picture) within a few hours!