Your pictures will be transferred for you on the date of the split. After that you will need to upload to the new rebranded site, if you're using DearDiary or OpenFiction.
I was going to resubscribe to DD Premium, does this mean I shoudl wait until the move is complete before subscribing?
The depends on who you ask :) I'd prefer you wait - Matt would probably rather you did it now ;-)
My diary is heavily illustrated with photographs. Of course, the photographs all have a URL at the current Album address, which apparently will be changing. Does this mean that when the switchover is complete, my several hundred images will be broken links?
At the date of the switchover, the address album.atomic-systems.com will remain valid, and your album will remain valid until your Premium Subscription expires. Depending on how long Matt can leave expired albums laying around it may last much longer than that...
However, once the dust settles I will work on a script that will automatically convert the URLs for you. So no, your images will not be broken, our intention is not to make extra work for our users :-) But a valid point nonetheless and one well worth asking - and one worth me adding a TODO item :-)
Steve.