You should put your image files in the assets folder. Then in your callback you can get the url to the image with app.get_asset_url('path/to/image.png'). The path param is relative to the assets folder.
You can make a seperate folder with the name “assets” and then to get the local image “IMAGE.png” which is in that folder to your app by using html.Img(src = app.get_asset_url ('IMAGE.png'). Further you can add any styling you want such as width, height etc.