You can make edits difficult but you cannot prevent them. For ex. one can take enough zoomed screenshots and combine them to get a high resolution image of the wanted parts and continues in Photoshop if he cannot extract images directly in Acrobat.
Using passwords and form structures is one (already said by others) way to create obstacles. Unfortunately cracking software exists, but a part of users surely beware installing such items. Another way is to build your images so that they splinter in bizarre way. Vector images and raster images can be rebuilt in a way that one easy to extract image contains unrelated elements, say 10 parts from one interesting image and other 10 parts of another and third interesting image.
Rasterize vector shapes with no extra resolution beyond the intended usage needs. Let all probably nice to extract parts have some background other than 100% white if possible.