Uploadcare

Uploadcare handles uploading, storing and processing files for you. All components of Uploadcare, from widget to CDN, work seamlessly together, require almost no configuration and allow maximum flexibility exactly when you need it.

Uploadcare consists of three components: Upload, Storage and CDN. Upload interfaces, such as browser widget and components for mobile applications, allow users to upload files. Whenever a file is uploaded, your application receives CDN link or file UUID which can be used by API to get detailed information about the file, store or copy it. Any file you’ve stored is available via CDN, which delivers original files to your users, as well as versions of them tailored for your needs: thumbnails and whatnot.

In order to use Uploadcare, you will need to sign up. Registration is free (no credit card required) and very easy, in fact, you can sign up with your Google or GitHub account, so you don't have to think up a new password. After successfully completing your registration, you will get public and private keys for your project that allow you to interact with the service.
More information: https://uploadcare.com/