A lot of the images we hosted on the server were uploaded while we were on the old phpBB2 software. The images were stored in a directory called userpix
I've migrated this directory onto the second server, and replaced all referenced to the old image URLs in posts to the new ones.
So, before, they would have been
https://z22se.co.uk/userpix/image.jpg
They are now
http://cdn.z22se.com/userpix/image.jpg
If these were linked from elsewhere on the web, I've added a redirect to force the image from the new URL
RewriteRule ^userpix/(.*) http://images.z22se.co.uk/userpix/$1 [QSA,L]
If you notice any of the older images not working, please let me know.