CHR already gave you a long list of reasons, so I'll just add to that.
Ranking is based on ~255 factors, including on and off page items. WB has a lot of internal linking across a lot of pages, plays in the dirty parts of the sandbox, and relies on a combination of a lot of the lower-value factors in the algorithm.
The problem with than approach is that you will get your arse handed to you if anyone competes on the fewer, more heavily weighted factors. Some unique content (text & images), a few local links in and out, proper site technology and architecture and you're golden.
This isn't a commercial, just a statement of fact: I'd put one of our Florist 2.0 sites up against any Wesley listing and expect to eat his lunch.
Wesley & those who market their sites in the same manner are on borrowed time.
The search engines do have technology to create a digital fingerprint for each image (and video). It's how the movie studios block a lot of copyrighted material from getting onto YouTube, and how copyrighting services identify stolen images. It's also how Google Image Search can identify pictures with a human face - or adult content.
The image name and alt text are the most important signals about an image, but the placement within your site and the surrounding content on the page are also important.
Ryan
