fixing the order of channel entries via category

Hi

I’ve got a load of images set in a channel, with each image having a category of landscape or portrait and I want to show 12 images in a sequence but need them fixed in order, .i.e landscape, landscape, portrait, landscape etc. Is there anyway to do this? At the moment I’m having to call each image with entry_id for each placeholder with its own channel entry code, but want this block of images to populate more dynamically as images are added.

Any ideas?

Thanks

Andy