How to upload images into the unity app from some external folder so that it is saved in the app for future reference?

I am making an app which requires to provide user with the facility to upload as many images which he has already got, from some external folder, such that the images remains saved in the application for him for any further use. It should be like using an image he has already got, and saving it into the resources folder or something feasible, so that that image is now a part of the application in his device. JavaScript solution would be appreciated.

Thanks in advance.