YouTube Thumbnail Maker: Create Free Custom Thumbnails | Adobe Spark
Thum.io | Fast real-time website screenshot API
10 Free Website Thumbnail Generation Services - Web Resources Depot
ThumbGettys: Free Video and Website Thumbshots Generator Service Provider
BitPixels - Website Thumbnails
Free and Paid Thumbnails for Websites
Free preview thumbnails on your site. Web page screenshot image
Thumboo! Free Website Thumbnails and PHP Script to Generate Web Screenshots
thumbalizr - a website thumbnail creator
WebSnapr - Website Thumbnails For Your Site