Looks indeed like a corrupted jpg. As far as I know IE does not recompress the images if your cache is small, that would mean the images you see would look worse if you view them again (high compression factor). Anyhow. It could be your ISP (or rather the proxyserver/cacheserver they use) that somehow has a problem with RR or has corrupted images in it's cache. In that case there's not much you can do about it. Since it happens in both IE and Firefox, you can pretty much rule our anything browser related.

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