For legal reasons, I need to be clear that I am not a lawyer or an attorney and this is not legal advice. However, I do have some experience as a graphic designer and a web developer, so what follows is from my own personal experience.
It is hard if not impossible to completely prevent someone technically from taking images that don’t belong to them if they are determined. After all, when the photos are digitally rendered in their final form, they have to be viewable by the computer or device and can therefore be intercepted and captured.
The best way to protect the intellectual property of the photographer is to choose a license which explicitly limits the use of the images themselves. This won’t prevent someone from taking the images if they want to, but it will make it clear that anyone who does so is doing so against your wishes and against the wishes of the photographer.
If you want to go a bit further, you could also share a link in your license or documentation back to the stock photos that you used so that people who like those images can buy them for themselves. It’s a nice way to share credit and to help support the people who create the resources that you use.
Hope that helps!