Using Gulp:
You can add a custom task:
gulp.task('images', function() {
return gulp.src(['app/assets/images/*'])
.pipe(gulp.dest('www/build/images'));
});
and then make sure you add it in the runSequence(s). e.g.
runSequence( ['images', 'sass', 'html', 'fonts', 'scripts'],
I also used ‘gulp-imagemin’ to compress the images. npm - gulp-imagemin