If you want to use images in your Android App you will need to put them in the drawable folder under the res directory.
Like on my System the path is /HelloAndroid/app/src/main/res/drawable
Android also gives you the option to put images for different screen densities.
For this you can create the following folders under drawable.
- android-ldpi : Low Density Screens around 120dpi
- android-mdpi : Medium – 160dpi
- android-hdpi : High Density – 240dpi
Source Code https://github.com/ankur-srivastava/HelloAndroid/blob/master/app/src/main/res/layout/ui_components.xml