maybe you could make some tests if you can't use the mentioned apache modules:

$points = 0;

whats the referer? does the user came from your homepage? good sign: $points++

is the useagent something you know (Internet Exploder, Gecko, Opera, Google) $points++

supports user agent javascript (most spambots don't do this) $points++

ip requested no page in the last x secs? $points++;

if ($points  > 1) {
    show_gallery();
}
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