I use a (not so well known) feature with Google AppEngine - Images API. It's pretty awesome as well. Works really well for web applications with basic image manipulation requirements.

https://cloud.google.com/appengine/docs/standard/python/imag...

The best part is, you call your image with specific parameters that'll do transformations on the fly. For example,

    <image url>/image.jpg?s=120

will return a 120px image. Appending -c will give you a cropped version, etc.