gulpfile.js

/*!
 * gulp
 * npm install gulp-ruby-sass gulp-autoprefixer gulp-minify-css gulp-jshint gulp-concat gulp-uglify gulp-imagemin gulp-notify gulp-rename gulp-livereload gulp-cache del --save-dev
 */
var gulp = require('gulp'),
    sass = require('gulp-ruby-sass'),
    autoprefixer = require('gulp-autoprefixer'),
    minifycss = require('gulp-minify-css'),
    jshint = require('gulp-jshint'),
    uglify = require('gulp-uglify'),
    imagemin = require('gulp-imagemin'),
    rename = require('gulp-rename'),
    concat = require('gulp-concat'),
    notify = require('gulp-notify'),
    cache = require('gulp-cache'),
    livereload = require('gulp-livereload'),
    del = require('del');

gulp.task('clean', function(cb) {
  del(['dist/assets/css', 'dist/assets/js', 'dist/assets/img'], cb)
});

gulp.task('images', function () {
    return gulp.src('assets/*.(png|jpg|jpeg|gif|svg)')
      .pipe(cache(imagemin({ optimizationLevel: 3, progressive: true, interlaced: true})))
      .pipe(gulp.dest('dist/assets/img'))
      .pipe(notify({ message: 'Images task complete'}))
});