A similar issue was discussed a while ago. Check it out: Images from image tag not loading in iOS emulator
Once you add the assets to your folder www/img be sure you include it in your project using this:
<img ng-src="img/picture.png" width="80">
Make sure there is no / before the src url. This fixed it for me.
Once you do this be sure to rebuild your app as @patrickdu mentioned. In your case substitute <platform> with android
Hope this helps.