I have been purchasing standard licences for any photos I use. I have referenced the authors in the front cover.
The school (not me) now wants to sell the books and therefore the images will need an extended licence.
My question is- do I purchase the licence myself as I am the only person that works with the file?
OR Does my school need to purchase the extended licence as they are the ones selling the product and the ones making money off it?
You do or the school does that's up to both of your and what is easiest to manage for you and the school. If you buy, make sure the school adheres to the license terms (small declaration for your records is enough). If they buy, they will anyhow agree with the terms.
In the case 1 You buy) the situation is like an agent doing some work for the school and part of that work is to acquire the rights to the image.
In case 2 The school buys) the situation is like they having the asset and asking you to do some work with that asset on their behalf.
Both situations are standard situations in this business.
Regards, Abambo Hard- and Software Engineer and Photographer.