As long as you follow the GPL license you can redistribute it, for free or at cost. Linux is mostly free as in freedom and usually free as in free beer.
Wikipedia says ElementaryOS has a pay what you want model. So if your image is from them then you don’t have to pay (a 3rd party is free to charge you for it - bandwidth ain’t free).
Ownership implies control - being able to maintain/repair, modify or even resell.
To be in control of software you need access to it’s source code, and have the right to share changes with others.