OK. You have two ways of working with images: either you need to translate it (caption, alternative text...) or not.
1. In the first case you have to upload your images as usual. A language will be affected to a language. And you need to go to the media table to add a translation for each media you add. Only the images that you have translated are available for the translated post.
2. If you don't need to translate the image caption and so on, then go to the Polylang settings and uncheck the media support. you will have no more language associated to your image and you will be able to use them as usual.
Note that in all cases, there is currently no way to automatically copy your images from the original post constent to the translated post content.