Thumbnails Cloud - The simplest API for generating file thumbnails
Headers.me - Create social cover images that get you followers
Blog Cover - Cover image generator for your blog post
Slickr - Powerful cover image generator for your Hashnode blog
Screenshot Bin - Generate website screenshots and thumbnails at scale, right from your app. Screenshots as a service.
Source Wireframe Kit - Library of 537 blocks for desktop and mobile prototyping