RGB and CMYK - big deal apparently!

I got my book back today:

It all looked good until I got to the pages with the big images on it...

As you can faintly see here, there is a book around the image

It is more obvious on the tortoise page:

The people at DPI said it would be okay, but I was a bit like 'No, this is for my Final Major Project it has to be perfect' Soooooooo I've got to sort my drawings out.
What the problem was I did my drawings in photoshop under RGB colour format, but the indesign file was in CMYK format.
So I've gotta sort them out and send them off again..