For working program need xclip. Install it

sudo apt-get install xclip

Fill credentials to sftp in config.ini

Compile go files go build -o sftp_uploader *.go or use compiled binaries.

Run:

$ ./sftp_uploader # for upload image from clipboard buffer
$ ./sftp_uploader -r # for upload image from stdin

Example with flameshot:

$ flameshot gui -r  | ./sftp_uploader -r