That's a toughie. Convert JPGs to PNGs and back? If the conversion tool doesn't give an error, it will surely corrupt the virus. (Discard the file if the conversion tool gives an error.)

Is that really something that needs to be checked actively? Maybe it's sufficient to keep logs and act on reports reactively. It depends on the case, really.

In reply to Re^3: prevent arbitrary code execution in images by ikegami
in thread prevent arbitrary code execution in images by bear0053

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