Encode to png and upload to CGI how?

I've followed the "Texture2D.EncodeToPNG" documentation on Unity Script References and everything is working fine. But now it needs to upload the screenshot to a CGI script. I just don't know where to start and how to do it.

I've followed many tutorials on how to upload pictures to a CGI script and tried many suggestions on the internet. I have no or little experience with html, php and perl so doing server side scripting is already hard enough.

What does the CGI need to contain to hold and read a bytes array form. I've already got my own server running with xampp and an cgi-bin in my htdocs folder.

I really hope you guys can help me with this. Every input on this matter is extremely appreciated. Thanks in advance!