Finally got it sorted, for anyone in the future looking to get a custom sharelink page for clients, or friends...
The file in question is a slice file - slice-s352abf1c96.png it is located in two locations;
you can edit this file but you are limited to the height of the original QNAP logo at the top, if you need to make it wider you can widen the canvas and make sure everything is still positioned on the far left hand side. Save this file and place it back into the above two locations.
If you didn't alter the width, everything should work as-is.
To make it work with a wider logo, under the following directories there is a css file that needs to be edited.
Search the script for "95px" it is under the background-position prefix for the slice-QNAP section.
Change the 95 to whatever the canvas width needs to be to fit your logo. This will change the length of the wrapper in the header.http://www.calgarysbestoil.com/images/screenshot.jpg
- IMG tag wouldn't work for some reason.
Once the NAS is restarted everything will revert, if you install the Autorun script that OneCD referenced earlier then you should be able to make a script to copy the files on startup, still working on that bit myself.
PS... I believe it only needs the httpd/shareLink location for both, but I did all the locations listed above anyhow. - This is confirmed, if you just change the httpd/shareLink locations it will automatically correct the cgi-bin files as well, at lease it is doing so on my system.
I am running the following autorun script at startup to successfully copy the files over during reboot;
cp /share/Public/logo/slice-s352abf1c96.png /home/httpd/shareLink/images/
cp /share/Public/logo/app.css /home/httpd/shareLink/css/
I'm not sure why, but if I didn't run a remove command they files weren't copying all the time. Sometimes it would just leave the original file in the location.