So recently I was asked to shoot for a multinational on a project they had their products on.

Essentially it was a heap of Architectural images where the brief was to make the building look more "regal". So I took the liberty to go crazy and well the client loves the images.
The images will be used in a promotional advertorial magazine that this company produces, which may be then used by head office for worldwide use. There is already an offer of further work every two months so I don't want to risk that by getting greedy.
My questions is they want 7 of the images and I gave them a hourly rate.
Now they are wondering the cost for the images.
So do I charge extra for the images on top of the time?
Or does the fact I charged an hourly rate mean they already own the copyrights and that's that?

I don't mind either way as I did charge a very high rate for a rank amateur.