High-anonymous (or elite) proxy never returns any "proxy" variables in reply to HHTP head request, nor your real IP address. If the remote host does not check incoming IPs against list of known proxies it can not detect the such type of proxy.
In a figurative sense, anonymous proxy says "I am a proxy" in HTTP headers. Your real IP address is not transmitted, but any host can detect (using the simplest algorithms) that you are using a proxy server.
Transparent proxies shows its IP address in 'REMOTE_ADDR' variable and your IP in HTTP headers in some variables (for example in 'HTTP_VIA').