So, you're trying to share some files with someone who only has access to an old version of Word. Or maybe that Microsoft-hating friend of yours who only uses WordPerfect. Perhaps you want that old-school ebook to be an epub, rather than .lit. For any of these problems, there are desktop apps that work, of course. However, sometimes you want to be able to do that within a program. If so, Doxument and the beautiful Doxument API are what you need.
Image processing probably isn't the most exhilarating part of creating a website, and a tool that could take care of all of that would definitely be appealing. Blitline is a cloud based image processing platform that works on a pay-as-you-go basis. The Blitline API allows users to submit thousands of jobs to be processed and pushed to their online photo storage service, using a simple JSON interface.
Google Cloud Vision API gives developers access to powerful image processing and analysis tools for use in any project. This tutorial on Google Cloud Platform shows followers how to use the API to detect faces in an image, and use the returned coordinates to draw a polygon around each face.