It has long been accepted that hotlinking is an evil practice that steals the bandwidth of others. And indeed it is a free bandwidth ride, and one that hardly ever is accompanied by credit for the originator of the image. So there is a kind of malicious satisfaction in changing the hotlinked image to something like, oh … maybe naked David Haselhoff playing with puppies.

But a new analysis by Bill Slawski of a paper from Google and a patent application from Microsoft calls this point of view into doubt. Slawski attempts to determine why some images rank better than others in search engines, when conventional considerations seem not to fully account for variations in ranking.

Unsurprisingly, surrounding text and anchor text in inbound links are probably the biggest factors in determining image relevance. But image sizes, relationship to other images, frequency of use, image quality, and other factors can play a part.

The most intriguing consideration, however, might be “number of websites that contain an identical image.” If the same image occurs many times, especially in conjunction with certain keywords, it is a plausible surmise that it might be an important image to people searching for those keywords. As Slawski reports:

Images that appear on more than one web site might be more relevant for a query term than images that only show up on one web site, or they could be considered less relevant.

The reasoning behind this isn’t described, but maybe the text associated with each showing of the image is compared, and if it is similar from one to another it might be considered relevant for the text used. If that text differs with each display, it might be considered less relevant.

Finding whether images are identical might mean looking to see if the images shown on different pages are actually at the same address. For example, the same picture maybe show on ten different web pages, but the image itself is at one address, such as:

Identical pictures that aren’t at the same address might be compared by electronically reducing them to a computer readable hash value and comparing them to each other.

Bottom line: when you serve up some mischief to hotlinkers you could be reducing your rank in image search results.


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