How Can You Identify a Proxy Type?

To find out a proxy type, please check its properties for numbers of active open ports: HTTP Proxy – ports 80,81,8080 or 3128; SOCKS – ports 1080 or 1081; FTP - port 21 mostly, but you cannot connect to the FTP Server without an FTP client. CGI Proxy is a web-page, it means the port number absence when you work with it.

It is important to keep in mind that port numbers mentioned here are open by default, so if there is some interference with the server work (at the experienced user level), port numbers can be changed.
In general, for defining a proxy type it is better to use a special software, such as the Proxy Helper (download here), to show not only a proxy type, but also the properties (country, region, rate, response to a request, etc.) of the selected server.