Advanced Tibia client editing - how to?

[Redan]

Hello there. As you probably noticed, some servers provide custom clients with some cool features like in-game cam recorders, various counters or even custom items in the context menus. I was just wondering how is it done? I don't expect any tutorial, I just want to know the idea.
Client decompilation? Any special software required? Is there any memory writer launched both with the client?

I could not find anything about it on OT related forums. Thank you in advance!

 

[Paulix]

there is a client called OTClient that is open source and everything can be edited

 

[Printer]

Otclient as suggested else you have to inject the client with dlls.

 

[Redan]

My bad, I forgot to let u know I do not mean OTClients. It's easy to recognize it. The "custom clients" I mentioned were edited original CipSoft clients.
DLL injection? Anybody could tell me more about it?

#edit
I found this: http://www.ntcore.com/files/inject2exe.htm#PortableExecutablefileformat2
Is it that hard :0