Just a quick shot: with the serendipity_event_Regexpmarkup event plugin (available in spartacus) you should be able to transfer that markup on the fly.
The plugin ships with a regexp subdirectory where you can create a new file like "thickbox.php" with a content like this:
Code: Select all
$regexpArray = array(
'<a href="\1" rel="lightbox"><img src="\1" alt="\2" width="300" /></a>'
This has to caveats:
1.) It does not automatically create a thumbnail. As you can see, the original image file will be used and just rendered with a smaller image size.
2.) The regexps are executed everytime the entry is displayed, unless you use the caching entryproperties plugin. If you use that, make sure to clear the cache so that the plugin can take action on a fresh cache.
3.) I did not test this since I was running out of time, but I hope it gets you started. The regexps are not destructible, if they are wrong, you can try until they work [if you clear the cache if 2.) applies].