That's a good effort, but it will not work in all cases. Many sites (photoisland, yahoo photos) use a CGI to pull images out of a database. Although these files do not have the correct extension, they still return a valid image MIME type. Plus, I could fool your pattern like this: http://www.perlmonks.org/?jpg. That probably wouldn't do anything bad, other than a broken image, but still.

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IndyZ