If you know the user is coming from google images, then you should find the searched keyword(s) in the same referrer string.

You need to urldecode the 'prev' parameter of the referrer, and then grab the 'q' parameter within that.

For php you could use this:

function get_vars($string)
{
 $ret = array();
 $v2 = split("[?&]",$string);
 foreach($v2 as $x1){
  $x = explode("=",$x1);
  $ret[$x[0]] = $x[1];
 }
 return $ret;
}
function get_var($var_name,$string)
{
 $a = get_vars($string);
 return $a[$var_name];
}
$referrer = $_SERVER['HTTP_REFERER'];
$prev = get_var('prev',$referrer);
$prev = urldecode($prev);
$q = get_var('q',$prev);
$var = str_replace("+"," ",$q);
echo "image search keywords:".$var."<br />";

But the solution you are looking for to track image search with google analytics can be very easily found on the web by using your favourite search engine.

From what I'm reading, a key step for using Google Analytics is adding images.google.com as a separate search engine - otherwise it is tracked merely as a referer.

References:
[code.google.com...] (see "Search Engine Configuration" section)
[joostdevalk.nl...]

Also note, the referer strings from Google Images can be extremely long - so some tracking software truncates the referer url, which drops the keywords so they're not available. If this is the case for anyone, they need to modify the analytics package they are using or get the supplier to do that.

thanks guys!

If one adds "images.google.com" as a search engine, beware of duplicating your traffic signals. If you are already using something like a bolean expression like: "URL contains google.com" as a search engine, then many analytics packages will now count those image search visitors twice.

You might want to add images.yahoo.com as well, if you want to track your image search keywords...