Michel Telendro describes that it has become a search engine optimization practice (black to gray-hat, I assume) of hotlinking images from other servers... to rank your own site well in Google Image search results.
How does that work? Well, you might have noticed that Google Images doesn’t just return pages from where a picture originates; for instance, querying Google Images for site:google.com, Google among other results shows a page from bbs.mydriver.com... which simply includes a JPG from somewhere at groups-beta.google.com. When you click-through to that page, it will then not be the origin site’s ads that will be displayed, of course, but the ads of MyDrivers.com, even though they likely don’t own the pic.
Michel, who tried this out, says “I do one of this hotlinking with one flickr image in a new domain (3 weeks, no backlinks) and in one week I was ranking #3 for that keyword in [Google Images].”
Case in point – do an image search for paris in Spanish Google, and of the top 5 results, all but 1 are hotlinking the image. Even when you do a Google web search, thanks to the direct image results box on top of the web results, a hot linker ranks top for paris. Michel says, “I think there are zillions of examples...”
Now, these aren’t all highly optimized spam sites, but partly just your average innocent blogs (and some may even hotlink because they pay the origin domain for hosting, though that’s certainly not true for all hotlinkers). Indeed, hotlinking an image without asking exposes your site to the risk of defacement; the image owner just needs to replace the picture with something shocking, and it will then display on your site.
Source:→ BlogoscopedGoogle, SEO, Hotlink, Images, Article