Suppose you have a favorite animation, it is a good way to learn a new language using the images and lines of the animation. However, those contents of animation are copyrighted by the company which made the animation. If another company wants to make a collection of example sentences using the animation lines, it must get permission from the company which made the animation. This plan is difficult to carry.
However, if you make learning materials for yourself, the story is different. In the case of personal use, the Japanese Copyright Law allows people to make copies. Most of the other countries have a similar article.
In other words, it is legal to duplicate images of your favorite animation on learning materials you use. On the other hand, it is illegal to sell it or make it available for download on the internet. That means you cannot get what you want from others. The possibility is very low. There is no choice but to make it yourself.