1. What it is and where to get it. This is a great bit of software to turn directories of long forgotten photos into an eaily accessable photo album.
2. ImageIndex, How I use it.
I sort out the pictures I want to add to Mythicalbeast placing them in a sub-directory directory. Running the following command generates the html and creates a medium sized jpg more suitable for downloading and also a thumbnail.
cd <source/directory>
imageindex -title "G-BCRR - various" -destdir ~/tmp/album -medium -forceregen
As I only want the medium sized images on Mythicalbeast. I do a quick hack 
I move all the files from the subdirectory album/medium overwriting the full sized images in album and then remove the now empty medium subdirectory. Then a quick edit to the file index.html to remove the links below each thumbnail the line I delete looks something like the following
<DIV CLASS="index"><A HREF="cockpit_right.jpg">full size</A> | <A HREF="medium/cockpit_right.jpg">medium</A></DIV>
Lastly I need to tweak the index.html page one level up.
Copy to my local temp area/web server to do a check all is as expected befor uploading to the live Mythicalbeast server.