Hi, I used to use Auto-Background Changer which is a free application to change the background of an image. It supports JPEG and PNG formats and is compatible with Android and iOS devices. I think it's perfect for you. However, if you want to read more information about such free apps to change image background, here is a link to the blog skylum.com/blog/best-apps-to-change-background
which I recently found. There you can learn about eight free applications and take the one you need.