I went on wireless between my two games and saw my character was an old fat man ;)
I know in Diamond/Platinum there was a guy who asks you what type of trainer you are, then yopu get their sprite. Is there the same thing in HG/SS?
In Violet city Pokecenter there is a guy standing on the left stairs leading to the wireless counter you talk to him and he'll ask you what Image do you want it to be and then he'll change it
As said by Sh7atoap, you go to Violet city pokemon center and a boy tells you how trainers see you. You could be a bug catcher, psychic, ace trainer etc...