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<p>I need to be able to detect if a used already visited a particular page. </p>

<p>I can set a cookies at their initial visit. I can also store some environment, such as IP, browser, OS, perhaps even language and create some string, like MD5 to compare against current visitor's environment. </p>

<p>Is there another method I should consider?   </p>

<p>I work with PHP.</p>
