How have a skin for a NPC

I would like to know how I can change the skin for a npc (I can modify bukkit if it need). To have a NPC like this (this server haven't Spout, laucher)

 

Probably Citizens

 

I think they used the minecraft skin database, if you name the npc to a player that exist it gets the skin of the player. I might be wrong but I believe they did it like that.

 

That is how it is done, yes.

 

Do you think it should be modified bukkit or it's a plugin ?

 

it can be done with a plugin

 

How I can do ? In the class Player they are no field for the skin ?

 

How do you spawn your NPC, for starters

 

thats because the client gets the skin from the name ill post some psuedo code from the mc source.
this is basically how it does it this is spread across 2 classes but w/e
url skin = "http://skins.minecraft.net/MinecraftSkins/" + nameofotherplayer + ".png"
connection con = skin.connect
image playerskin = image.load(connection.input)

 

The skin configuration is only on the client ? we can't send an skin url ?

 

no the client gets the skin from the player name.
when you code mods you come across these things.