I've been searching for a while with no luck, I'm a new user to Silverstripe.
I don't usually use prebuild CMS solutions these days but a friend approached me to move a system for her, from one server to another and it happens to be Silverstripe, so I've been figuring it out for her.

The site has moved over fairly smoothly as far as I can tell so far, other than a small issue with the images on her site not showing up now.
The links look to be correct (it's looking in the right place) but it seems to be not finding them.

What should the CHMOD on the assets directory be? 777? Or something else?

Also, is there a specific document to guide you through moving servers?
Any advice, gratefully accepted as potentially there is a step I've missed somewhere being that I don't know this software at all!

Process was fairly standard, site backup, db backup, upload files, upload db to new db, edit config file accordingly, CHMOD assets directory.

You pretty much did a textbook migration so everything sounds right. The deprecated function sounds like you might be using an outdated module. Upgrade all the modules if possible.