Fotomat 
Fotomat is an extremely fast image resizing proxy, enabling on-the-fly resizing and cropping of JPEG, PNG, GIF, and WebP images. Written in Go and using the fast and flexible VIPS image library, it aims to deliver beautiful images in the shortest time and at the smallest file size possible.
Documentation
See features, building instructions, command-line
flags, and
benchmarks.
There's also API detail for Fotomat's thumbnail, format, and vips wrapper libraries.
License
Copyright 2013, 2014, 2015, 2016, 2017, 2018 Aaron Hopkins and contributors
Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at: http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.