Watermarker is a simple web service for adding watermark to your pictures.
To use this service, you need to upload two files, a png watermark file, and a zip file contains the pictures. The server will return a zip file, which contains pictures that have watermark added.
To run this program, you need to install ffmpeg on your server first, then
run go run watermarker.go and open http://[SERVER-IP]:8848 in your browser.