Advanced Image Sitemap is a plugin for WordPress by makong is a sitemap generator which scans your website for all images, and create structured XML sitemap file.
Image XML sitemap gives Google (and other search engines like Bing) meta data about pictures on your website, so SE could crawl and index all of them. If all your pictures are indexed by Search Engines you are getting more chances to take a part in Image Search.
You can create template for image titles and descriptions (based on file name)
You can add custom location for all your images
You can include in Image Sitemap your thumbnails
You can exclude images from sitemap by their size
You can exclude images from WP plugins
More info: https://wordpress.org/plugins/advanced-image-sitemap/