Is it possible to preserve user ip address with transparent proxy?

Currently it seems to add an http header with original address, but i'd like that the connection appeared from the client's address.

I don't think its possible to preserve the user's IP address when using any kind of proxy or NAT configuration.

Most webservers should be able to retrieve the originating IP address from the HTTP headers, like they do on this page: http://www.whatismyproxy.com/

You might be able to preserve the user's IP address when you do ARP spoofing, but then you'll have to intercept all the user's data. I'm no expert in this field, so don't just take my opinion in this matter.

I don't think its possible to preserve the user's IP address when using any kind of proxy or NAT configuration.

it is possible. Balabit TProxy. it should already be in mainstream kernel and squid versions, I believe