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When you look at the HTML-source, the img-tags (including the 'width=22', etc) are still there.
But dblobaum could be right about a Google directory update.
Now I don't see these images anymore. The only reason I can think of that these images are sometimes shown, and then disappear, is 'load balancing' which also causes the everflux. So if some data centres have the image and others have not, it is sometimes visible and sometimes not. Why are these gif-files missing in some data centers? I don't know. Is there a relation with updating with data from new RDF dump? You can only speculate.