Hi,
First, I made myself two png pictures - one saying "New page" in red, the other "Page exists" in green.
Then I copied the doku.php script to image.php and replaced the 404 part and the remainder with a condition to display either this or that picture.
And it worked like a charm, now I have log alert emails with indication if the page for the exception has been created already.
To make use of it I have
<a href="http://theserver/doku.php/thepage"><img src="http://theserver/image.php/thepage" alt="thepage" /></a>
in my emails
I can imagine this could go much further and become a proper plugin - possibly utilising GD to give more details, or static pictures as a fall-back solution if GD is not available - but have no resources to implement it.
To be honest I was quite surprised how simple that was!
This is the image.php shortened:
<?php
// include the standard part of doku.php up to the 404 handling:
// (send 404 for missing pages if configured...)
// then replace the rest of the script with:
if($INFO['exists']) $img = 'wikipage-exists.png';
else $img = 'wikipage-new.png';
$fp = fopen($img,'r');
header('Content-Type: image/png');
fpassthru($fp);
fclose($fp);
?>